ISO 286 Fits Explained: H7/g6, Transition, and Interference for CNC Parts (2026 Edition)

ISO 286 defines size tolerances for cylindrical mating features by combining a letter for tolerance zone position with a number for zone width. At Ø25, an H7 hole sits between 25.000 and 25.021 mm; pairing it with a g6 shaft gives you 7 to 41 µm of clearance, an H7/p6 press fit gives 1 to 35 µm of interference, and an H7/s6 medium drive fit gives 14 to 48 µm. The gap between “the drawing calls H7” and “the shop delivers H7 in one setup” decides whether your part ships or reworks: a Ø30 H7 bore hit with a boring bar plus a finish reamer avoids the grinding step, and EPOC CRAFTER holds ±0.05 mm on critical CNC features without a grinder. This guide is Part 1 of the drawing tolerancing series; siblings cover surface roughness, ISO 2768, and thread callouts. It covers ISO 286-1:2010 notation, the Ø25 numeric bench for ten common fits, hole-basis versus shaft-basis selection, CNC-achievable IT grades, Shigley’s interference-fit contact pressure with the corrected radial substitution, SKF bearing seat recommendations, and a Six-Check Fit Selection framework.

1. What ISO 286 Actually Specifies

ISO 286 specifies the ISO code system for size tolerances on cylinders and pairs of parallel opposing surfaces. It defines 20 tolerance grades (IT01 through IT18), 28 fundamental deviation positions per feature type, and the hole-basis and shaft-basis conventions used to build fits. For the full drawing framework this sits inside, see how to tolerance a CNC drawing.

ISO 286-1:2010 covers nominal sizes from below 3 mm up to 3 150 mm. It applies to two feature types only: a cylinder, and two parallel opposite surfaces (a slot width, a key thickness). Anything outside those shapes falls under other GPS standards.

The system has three moving parts. The standard tolerance grade sets zone width and comes from the IT number: IT01 (tightest, gauge-block territory) through IT18 (rough, structural steel). The fundamental deviation sets where the zone sits relative to nominal and comes from the letter: uppercase A through ZC for holes, lowercase a through zc for shafts (the letters I, L, O, Q, W are skipped to prevent confusion with digits). The basis system picks which mating feature has zero deviation from nominal: hole-basis (letter H, EI = 0) dominates production; shaft-basis (letter h, es = 0) shows up when stock shafting or hardened shafts fix the shaft first.

If you are starting a new mating pair machined in-house on CNC, pick hole-basis with H7 on the hole and g6/h6/k6/p6 on the shaft. That covers most cases at the lowest cost, because precision CNC turning adjusts an outside diameter faster than reaming or grinding adjusts a bore.

2. Reading the Callout: Letter Sets Position, Number Sets Width

In a callout like Ø25 H7/g6, the uppercase H marks the hole with a fundamental deviation of zero, the 7 sets the hole zone width, the lowercase g marks the shaft with a negative fundamental deviation, and the 6 sets the shaft zone width one grade tighter than the hole.

Decoding a fit is a two-step read. First the letter fixes the zone position. Second the number fixes the zone width from ISO 286-1 Table 1.

For H7 at Ø25 (which falls in the 18 to 30 mm size range), EI = 0 places the lower limit at 25.000 mm, and the IT7 grade sets a 21 µm zone width; the upper limit lands at 25.021 mm. For g6 at Ø25, the fundamental deviation es = -7 µm places the upper limit at 24.993 mm, and the IT6 grade sets a 13 µm zone; the lower limit lands at 24.980 mm.

The shaft is one grade tighter than the hole in almost every preferred fit (H7/g6, H7/h6, H7/k6, H7/p6). ISO 286-1 pairs them this way because a shaft OD is easier to hit on a lathe than a bore is on a boring bar or reamer, so you buy the extra grade on the cheaper feature.

If you loosen the pair from IT7/IT6 to IT8/IT7, you widen the total fit range from 34 µm to 55 µm and save roughly one finish pass in the bore. You also remove the sliding-fit character and turn the assembly into a loose running fit. Loosen only when your mating function tolerates the extra clearance in operation, not to save cycle time on the drawing. Dimensions on the same drawing that don’t mate anything fall under the general tolerance class in the title block, not ISO 286 the two systems govern different features on the same part. Threaded features carry their own class-6H/6g tolerancing that runs parallel to ISO 286; when your part has both a bearing fit and a tapped hole on the same face, keep the two callouts separate and match thread engagement length to the joint’s load class.

3. Three Fit Categories: Clearance, Transition, Interference

A clearance fit always leaves space (H7/g6 gives 7 to 41 µm at Ø25). A transition fit overlaps the zones so assembly yields either small clearance or small interference (H7/k6 covers -15 to +19 µm at Ø25). An interference fit always overlaps (H7/p6 gives 1 to 35 µm interference).

Clearance fits let you allow relative motion, thermal expansion, or a lubrication film. The tightest ISO 286 clearance for a Ø25 pair is H7/h6, with zero minimum clearance and 34 µm maximum. Beyond that, H7/g6 sliding, H8/f7 close running, H9/d9 free running, and H11/c11 loose running widen the gap into hundreds of micrometres. Sealing surfaces, sliding valve stems, and precision guides sit here.

Transition fits aim for accurate location while accepting a small unpredictable clearance or interference. H7/k6 and H7/n6 at Ø25 both sit here, but their overlap sits on opposite sides of the zero line: k6 leans toward clearance (max clearance 19 µm, max interference 15 µm) and n6 leans toward interference (max clearance 6 µm, max interference 28 µm). Do not use a transition fit for a rotating bearing race or a sealing feature; the batch will split between clearance and interference and half your parts will not match design intent.

Interference fits transmit torque or axial load through friction from elastic deformation. H7/p6 (1 to 35 µm interference at Ø25) lets you assemble by arbor press at room temperature. H7/s6 (14 to 48 µm) usually needs a thermal shrink method (heat the hub, freeze the shaft). H7/u6 (27 to 61 µm) is permanent; disassembly damages both parts.

For a Ø25 locating dowel that must resist vibration but stay removable in service, choose H7/k6 with a soft-mallet assembly and a puller for removal, not H7/p6 which needs an arbor press and risks galling on repeat cycles. The exception is when you disassemble once a year or less; H7/p6 then gives a more secure joint and the annual press job is acceptable.

4. Ø25 Reference Table: What Each Fit Actually Delivers

At Ø25 nominal, an H7 hole runs 25.000 to 25.021 mm. Pairing it with ten common shaft classes covers the full range from H11/c11 (110 to 370 µm loose clearance) to H7/u6 (27 to 61 µm force interference), with H7/g6 sliding, H7/k6 transition, and H7/p6 light press as the three most used points.

Table 1. Ø25 fit calculations for ten preferred hole-basis combinations (ISO 286-2:2010, 18 to 30 mm range).

Fit	Hole limits (µm)	Shaft limits (µm)	Min result	Max result	Fit character
H11/c11	0 / +130	-110 / -240	+110 clr	+370 clr	Loose running
H9/d9	0 / +52	-65 / -117	+65 clr	+169 clr	Free running
H8/f7	0 / +33	-20 / -41	+20 clr	+74 clr	Close running
H7/g6	0 / +21	-7 / -20	+7 clr	+41 clr	Sliding
H7/h6	0 / +21	0 / -13	0	+34 clr	Location clearance
H7/k6	0 / +21	+2 / +15	-15 int	+19 clr	Transition, toward clearance
H7/n6	0 / +21	+15 / +28	-28 int	+6 clr	Transition, toward interference
H7/p6	0 / +21	+22 / +35	-35 int	-1 int	Light press
H7/s6	0 / +21	+35 / +48	-48 int	-14 int	Medium drive
H7/u6	0 / +21	+48 / +61	-61 int	-27 int	Force / shrink

clr = clearance, int = interference. Values calculated from ISO 286-1 Table 1 (IT grades) and ISO 286-2 fundamental deviation tables for the 18 to 30 mm range.

To read a row for another nominal diameter, look up the IT grade width for that size range in ISO 286-1 Table 1 (for Ø10, IT7 = 15 µm; for Ø50, IT7 = 25 µm), then apply the fundamental deviation letter from ISO 286-2. The pattern stays constant: H7 hole always runs from 0 to +IT7, and the shaft position shifts by the letter’s fundamental deviation.

For a Ø25 pair that must slide under load, pick H7/g6; the 7 µm minimum clearance holds free motion under thermal expansion of about 3 µm for a 10 °C rise in aluminum, and the 41 µm maximum keeps radial play under 0.002 mm per mm of diameter. Do not substitute H7/h6 for the same function; the zero minimum clearance means half the batch will bind on assembly if either surface carries a light burr or dust film. If you have an aluminum bracket exposed to a 40 °C shop-to-service temperature swing, size the pair from the hot end and verify surface finish against surface finish requirements for fits, because a Ra 3.2 µm shaft consumes about 5 µm of the calculated clearance in the first hour of run-in.

5. Hole-Basis vs Shaft-Basis: When Each Is Cheaper

Hole-basis (H hole with varied shaft letter) dominates production because a shaft OD is faster to adjust on a lathe than a bore. Shaft-basis (h shaft with varied hole letter) applies when stock shafting fixes the shaft first, or when a hardened shaft cannot be re-machined.

Your choice follows what feature the shop can adjust after measurement, not designer preference.

In hole-basis, the H hole runs at zero fundamental deviation, so it comes off a standard reamer (H7, H8), and you turn the shaft to the letter grade that produces the target fit. This matches how precision CNC turning and boring work in production: a boring bar plus a finish reamer produces H7 on the first pass, and the lathe trims the shaft in 5 to 10 µm increments until the fit lands.

Shaft-basis, with h at zero fundamental deviation, applies when the shaft is fixed before machining. Cold-drawn round bar arrives at h9 or h11, ground bar at h6, and a shaft hardened to 45 to 50 HRC cannot be turned again without carbide inserts and much slower feeds. The hole absorbs the fit adjustment, and callouts read F7/h6, K7/h6, P7/h6 instead of H7/f6, H7/k6, H7/p6.

Table 2. Basis selection by scenario.

Scenario	Preferred basis	Why this basis costs less
New design, both parts machined in-house	Hole-basis (H7 + g6/h6/k6/p6)	Standard reamer holds H7 on first pass; the lathe adjusts your shaft in 5 to 10 µm increments
Off-the-shelf rolling bearing on a shaft	Hole-basis (housing letter varied)	Bearing OD is fixed by ISO 492 as an h-basis element; your housing bore absorbs the fit
Ground round stock as a shaft (h6, h7)	Shaft-basis (h + F7/G7/K7/P7 hole)	Your shaft dimension is purchased, not machined; the hole absorbs the variation
Shaft hardened above 45 HRC before assembly	Shaft-basis	Hard turning or grinding after heat treat costs 3 to 5 times more per pass than boring the mating hole

According to Dewey Wu, general manager at EPOC CRAFTER: on a Ø30 H7 bore, one pass with a boring bar followed by a hand-fed finish reamer holds the top and bottom limits within 15 µm on the first setup, whereas re-machining the shaft after an out-of-spec bore adds a second setup and 8 to 12 minutes per part.

If you have a mixed assembly where one shaft mates with three different features (a rolling bearing seat, a pulley bore, and a keyed hub), shaft-basis wins even when the shaft is machined new. Keeping the shaft at h6 lets you vary the three holes (K7, N7, F8) with standard drill-and-ream tooling instead of turning the shaft to three different diameters.

6. CNC-Achievable IT Grades Without Grinding

CNC turning and boring reach IT7 on features up to Ø50 mm without a separate grinding operation, if the finish pass runs with a sharp insert and adequate coolant. IT6 needs honing or a slow finish pass; IT5 and tighter require grinding or lapping.

Not every H letter and number combination is producible in one setup. Each machining process carries a natural IT band; pushing tighter than that band drives cost through the roof or forces a second operation on a different machine.

Table 3. Machining process vs comfortable IT grade range.

Process	IT range	Notes for H7-class work
Drilling (twist drill)	IT10 to IT13	Prep hole only; never a finished H-tolerance bore
Rough milling	IT10 to IT13	Structural features, not fits
Rough boring	IT9 to IT11	Prep for finish boring or reaming
Turning (finish)	IT7 to IT9	Meets H8 shaft; H7 needs a slow finish pass and a fresh insert
Boring (finish)	IT7 to IT8	Meets H7 bore on Ø18 to 50 mm with a rigid bar and one finish pass
Reaming (H7 reamer)	IT7	Standard reamer produces H7 directly; adjust for size only
Grinding (cylindrical)	IT5 to IT6	Required for H6 shafts, hardened surfaces, or high-precision bearing seats
Honing	IT5 to IT6	Bore finish after grinding; also for Ra under 0.4 µm
Lapping	IT3 to IT5	Gauge blocks, seal-face flatness

Two implications drive practical fit selection. An H8 bore paired with an f7 or g7 shaft removes reaming and lets a single finish boring pass handle the hole, saving 30 to 60 seconds per part compared to a bore-plus-ream cycle. An H6 callout on a bore signals grinding, which means two-machine setup (mill or lathe first, then grinder) and typically triples cycle time.

According to Dewey Wu: on a Ø30 H7 aluminum bore, a boring-then-reaming cycle finishes in one setup on a mill-turn machine and holds ±0.010 mm inside the 21 µm IT7 window; moving that same feature to H6 forces a transfer to a cylindrical grinder and roughly triples per-part cycle time. Our precision CNC machining line holds ±0.05 mm on critical features without grinding, which covers all H7 fits from Ø10 through Ø100. Verify tool selection against the DFM design guidelines before locking the process.

7. Interference Fits: Contact Pressure, Assembly Force, Thermal Method

An interference fit generates contact pressure from elastic deformation of hub and shaft. For a Ø25 H7/p6 steel-on-steel joint with 9 µm mid radial interference and a hub OD of 50 mm, contact pressure reaches about 56 MPa and axial assembly force reaches about 16.5 kN with a dry friction coefficient of 0.15.

The contact pressure at the mating interface comes from Shigley’s Mechanical Engineering Design, Equation 3-56, which for same-material solid-shaft geometry simplifies to:

p = E · δ · (r_o² − R²) / (2R · r_o²)

Here δ is the radial interference (half the diametral interference), R is the nominal radius, and r_o is the outer radius of the hub. For a Ø25 shaft in a hub of 50 mm OD (R = 12.5 mm, r_o = 25 mm) with steel-on-steel E = 207 GPa and mid interference δ = 9 µm, the equation returns 56 MPa.

Engineering note: when you use radii, δ must be the radial interference; when you use diameters, δ must be the diametral value. Substituting the diametral value into the radii form doubles the calculated pressure. Dimensional check your inputs before you lock a hub design.

Axial assembly force follows F = 2π R L µ p, with µ = 0.10 to 0.15 for dry steel-on-steel and 0.05 to 0.08 with oil.

Table 4. Ø25 interference fit results (solid steel shaft, steel hub, r_o = 25 mm, L = 25 mm, µ = 0.15, E = 207 GPa, ν = 0.29).

Fit	Interference (µm, diametral)	Mid δ (µm, radial)	Contact p (MPa)	Assembly F (kN)	Method
H7/p6	1 to 35	9	56	16.5	Arbor press, room temp.
H7/s6	14 to 48	15.5	96	28.3	Thermal shrink or heavy press
H7/u6	27 to 61	22	137	40.3	Thermal shrink

Thermal assembly avoids the peak force and reduces galling risk on repeat cycles. To open a Ø25 steel bore by 18 µm (the mid-diametral interference for H7/p6), you heat the hub by roughly 60 °C above ambient using ΔD = D · α · ΔT with α = 12e-6 /°C for steel. For H7/s6 at the same diameter, heat by 100 to 110 °C to open the bore by 30 µm and leave a working clearance of 15 µm during insertion.

According to Dewey Wu: for our low-volume production runs with steel gears on steel shafts at Ø30 H7/s6, we heat hubs to 120 °C in an oven, hold for 15 minutes, and drop the hub over the shaft in one motion; the resulting joint transmits full torque without a key on shafts up to 40 mm.

Choose H7/p6 with an arbor press when your target axial force stays under 40 kN and the hub wall is at least half the shaft diameter thick; choose H7/s6 with thermal assembly when the joint must resist axial loads above 50 kN or transmit torque without a key. The exception is thin-walled hubs where r_o/R falls below 1.5: the pressure equation predicts hub yielding above 60 percent of material yield stress, and you must de-rate to H7/n6 or reinforce with a heavier hub.

8. Bearing Seat Fits: SKF-Recommended Selection

SKF fit recommendations depend on ring rotation, load class, and shaft diameter. For a rotating inner ring under light load on a Ø17 to 100 mm steel shaft, j6 is standard; under normal to heavy load in the same range, k5 or k6 applies; stationary inner rings use g6.

Rolling bearings carry their own tolerances per ISO 492, so the seat tolerance on your shaft or housing determines the assembled fit. The controlling variable is which ring rotates relative to the applied load, not the shaft speed itself. For North-American drawings, Machinery’s Handbook 32nd edition documents the parallel ANSI/ASME B4.2 metric fit system with letter symbols identical to ISO 286.

Table 5. SKF-recommended shaft tolerance for radial ball bearings (SKF Rolling Bearings 17000/1 EN, Table 5).

Condition	Shaft Ø (mm)	Shaft tol.	Radial run-out	Ra target (µm)
Rotating inner ring, light load (P <= 0.05 C)	<= 17	js5	IT4	0.4
Same, light load	> 17 to 100	j6	IT5	0.8
Same, light load	> 100 to 140	k6	IT5	1.6
Rotating inner ring, normal to heavy (0.05 C < P <= 0.1 C)	> 17 to 100	k5	IT4	0.8
Same, normal to heavy	> 100 to 140	m5	IT4	0.8
Stationary inner ring, axial displacement wanted	all	g6	IT5	1.6
Stationary inner ring, no displacement needed	all	h6	IT5	1.6

For a Ø30 rotating shaft carrying a light radial load under 5 percent of dynamic capacity C, choose j6; the 5 µm max interference holds the inner ring against creep without pinching the internal clearance. Do not substitute k6 in this range unless load rises above 0.05 C, because k6 at Ø30 adds up to 15 µm interference and can reduce radial internal clearance below the manufacturer minimum. Housing bores follow parallel logic in SKF’s tables; non-split steel housings for stationary outer rings under stationary load land at H7 in most sizes.

9. The Six-Check Fit Selection Framework

Six checks decide the fit for any cylindrical mating pair: function of the joint, load direction and magnitude, assembly method available, thermal environment during service, mating surface finish, and disassembly needs. Running them in order narrows any ISO 286 callout to one preferred code combination in under two minutes.

1. Function. Does the joint transmit rotation, transmit torque, locate a part, or seal a boundary? Rotation and sliding push toward clearance (H7/g6, H8/f7). Torque without a key pushes toward interference (H7/s6 or H7/u6). Locating without motion picks transition or light interference (H7/k6, H7/n6, H7/p6).

2. Load direction and magnitude. Rotating inner ring under load calls for interference on the inner ring seat (see Table 5). Load below 0.05 C accepts j6; above 0.10 C moves to k5 or m5.

3. Assembly method. An arbor press caps effective force near 40 kN in most job shops, which limits Ø25 steel joints to H7/p6 (16.5 kN required) or lighter. Above that, plan thermal shrink (heat the hub to 100 to 120 °C) or hydraulic assembly on a tapered seat.

4. Thermal environment. Steel expands 12 µm per metre per °C, aluminum 23 µm per metre per °C. For a Ø50 aluminum housing over a Ø50 steel shaft exposed to a 40 °C swing, differential expansion consumes 22 µm of clearance. Size at the hot end of the service range.

5. Mating surface finish. Sliding surfaces at H7/g6 need Ra 0.8 µm or finer. Interference surfaces at H7/p6 or tighter need Ra 1.6 µm or finer; rougher shafts lose 20 to 30 percent of nominal interference in the first assembly cycle from asperity flattening.

6. Disassembly needs. If your service manuals call for annual bearing replacement, cap the fit at H7/k6 for transition or H7/p6 for light interference; both allow puller-based removal without damaging the hub. H7/u6 is permanent.

Apply the six in order, not in parallel; earlier answers constrain later ones. For a Ø30 rotating shaft in an aluminum housing that must survive 40 °C thermal swings, function (torque) plus check 4 (thermal) forces H7/k6 rather than H7/p6, because H7/p6’s minimum interference of 1 µm would drop to negative clearance at the hot end. Skipping check 4 is the most common source of over-tight fits in outdoor equipment and consumer electronics enclosures.

Frequently Asked Questions

Q1. What are the min and max clearances in an H7/g6 fit at Ø25 mm?

H7/g6 at Ø25 gives you 7 µm minimum clearance and 41 µm maximum. The 7 µm comes from hole minimum limit 25.000 minus shaft maximum limit 24.993; the 41 µm comes from hole max 25.021 minus shaft min 24.980. Both values come from ISO 286-2:2010 tables for the 18 to 30 mm range. These bounds hold across any Ø25 H7/g6 pair regardless of material, but you lose 5 to 8 µm of usable clearance on rougher shafts (above Ra 1.6 µm) in the first assembly cycle from asperity flattening. The pair supports sliding motion, hand assembly without a press, and thermal expansion up to about 30 °C in steel or 20 °C in aluminum before it closes to zero.

Q2. Can CNC hold H7 without a grinder or a reamer?

Finish boring on a modern CNC lathe or mill-turn machine holds H7 on bores from Ø10 to Ø100 mm without grinding, if your finish pass runs with a sharp carbide insert, adequate coolant, and rigid tool overhang under 4x diameter. A finish reamer produces the same H7 window in shorter cycle time and is preferred above Ø8 mm when your material accepts reaming (aluminum, brass, mild steel, 304 stainless). Reaming loses its edge advantage in high-silicon aluminum, 316L and above, or hardened steels above 35 HRC, where finish boring with a coated insert gives you more predictable size.

Q3. How do I choose between H7/p6 and H7/s6 for a press fit?

H7/p6 is a light press with 1 to 35 µm interference at Ø25, assembled by arbor press at room temperature (roughly 16.5 kN required) and removable with a puller. H7/s6 is a medium drive with 14 to 48 µm interference, requiring thermal shrink (heat the hub to 100 to 120 °C) or a heavy hydraulic press, and disassembly typically damages the hub. Choose p6 when service disassembly is planned, when the joint transmits torque below 100 N·m at Ø25, or when hub OD is less than 1.8x shaft diameter. Choose s6 for torque above 100 N·m, for permanent joints, or when a key or spline is not acceptable.

Q4. What surface finish should mate to an H7/g6 shaft?

Sliding fits at H7/g6 require both mating surfaces at Ra 0.8 µm or finer to keep the calculated clearance intact through the first hundred operating cycles. A Ra 3.2 µm turned shaft mating a Ra 1.6 µm reamed bore loses about 5 µm of clearance in the first run-in, which drops a Ø25 H7/g6 pair from 7 µm minimum clearance to 2 µm and risks binding. Interference fits at H7/p6 or tighter tolerate Ra 1.6 µm because the interference itself flattens asperities on assembly, but a hub bore rougher than Ra 3.2 µm loses 20 to 30 percent of nominal interference in the first press cycle.

Q5. What is the most common mistake when specifying an ISO 286 fit on a CNC drawing?

The most common mistake is specifying an interference fit tighter than your assembly method supports. You call H7/s6 or H7/u6 on a Ø50 hub, then the shop discovers the arbor press hits its 100 kN limit before the joint seats, and the assembly requires a hydraulic press or an oven that was not planned. The second most common mistake is missing thermal environment: an H7/p6 fit sized at room temperature drops to zero interference when an aluminum housing over a steel shaft heats by 30 °C, letting the joint spin under load. Both errors are caught by running the six checks from Section 9 before locking the callout.

Q6. How do I substitute Shigley’s Eq. (3-56) without doubling the pressure?

Use one convention end-to-end. If you use radii (R, r_o, r_i), δ must be the radial interference (half the diametral value). If you use diameters (d, d_o, d_i), δ must be the diametral interference. Mixing the two doubles the result. For Ø25 H7/p6 with mid-diametral 18 µm, either take δ_radial = 9 µm with R = 12.5 mm (result 56 MPa) or take δ_diametral = 18 µm with d = 25 mm (also 56 MPa). Both routes give the same physical answer. If your number lands at 111 MPa, you mixed conventions.

Related Resources

Related Article: Surface Roughness Chart for CNC Parts. Ra target values for H7/g6 sliding pairs, H7/p6 press pairs, and how your process choice sets achievable roughness.

Related Article: ISO 2768 General Tolerances. What to write in your title block so unmarked dimensions on the same drawing do not fight the H7/g6 callouts.

Related Article: Metric Thread Chart and Tapped Hole Callouts. Thread engagement, tap drill sizes, and how thread callouts separate from cylindrical fit callouts on the same feature.

Related Pillar: How to Tolerance a CNC Drawing. The three-layer decision framework this article’s fit codes fit into.

Related Capability: Precision CNC Machining. Turning, milling, and boring at ±0.05 mm on critical features and H7 fits without grinding on standard aluminum and steel grades.

Related Standards Reference: Tolerances and Standards. ISO 286-1:2010, ISO 286-2:2010, ASME B4.1, ASME B4.2, ISO 21920, ISO 8015 mapped to inspection sheets.

Downloadable resource: Request the Ø-Segmented Fit Reference Chart (PDF) covering Ø3 through Ø500 for the ten preferred hole-basis combinations shown in Table 1. Email the address on our contact page with subject “Fit Reference Chart”.