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Ball Screw Shaft-End Machining Tolerances — Fits, Keyway, Circlip Groove, Locknut Threads & Roughness | MOSIONX

Machining standards we work to on MOSIONX ball-screw shaft ends: shaft tolerance zones (GB/T 1800.1), keyways (GB/T 1095), circlip grooves (GB/T 894), locknut threads (GB/T 197 / KM series), spanner flats, surface roughness (GB/T 1031) and runout limits (GB/T 17587.3) — full dimension tables in mm.

Every ball screw we ship is finish-machined to the shaft-end drawing you send us. The tables below are the tolerances our shop actually works to — shaft fits, keyways, circlip grooves, locknut threads, spanner flats, surface finish and runout limits — each tied to the GB/T standard behind it. Use them to specify your shaft ends, or send the drawing and we will quote to it.

On this page

Shaft-diameter tolerance zones (GB/T 1800.1-2020 / ISO 286-1)Parallel-key keyway dimensions and tolerances (GB/T 1095-2003)Circlip (retaining ring) groove dimensions (GB/T 894-2017, type A)Shaft-end locknut thread dimensions and tolerances (GB/T 197-2018 / GB/T 9160.2)Shaft-end spanner flats (reference dimensions)Surface roughness requirements (GB/T 1031-2009)Runout inspection limits (GB/T 17587.3) — C5 ground / C7 rolledCoaxiality / circular runout tolerance values (GB/T 1184-1996)General tolerances for linear dimensions (GB/T 1804-2000)General tolerances for straightness and flatness (GB/T 1184-1996 / ISO 2768-2)

1. Shaft-diameter tolerance zones (GB/T 1800.1-2020 / ISO 286-1)

Basic size (mm)h5h6 (common)h7 (common)g6 (common)f7 (common)d9e8h8h9
>6–100/-0.0060/-0.0090/-0.015-0.005/-0.014-0.013/-0.028-0.040/-0.076-0.025/-0.0470/-0.0220/-0.036
>10–180/-0.0080/-0.0110/-0.018-0.006/-0.017-0.016/-0.034-0.050/-0.093-0.032/-0.0590/-0.0270/-0.043
>18–300/-0.0090/-0.0130/-0.021-0.007/-0.020-0.020/-0.041-0.065/-0.117-0.040/-0.0730/-0.0330/-0.052
>30–500/-0.0110/-0.0160/-0.025-0.009/-0.025-0.025/-0.050-0.080/-0.142-0.050/-0.0890/-0.0390/-0.062
>50–800/-0.0130/-0.0190/-0.030-0.010/-0.029-0.030/-0.060-0.100/-0.174-0.060/-0.1060/-0.0460/-0.074
>80–1200/-0.0150/-0.0220/-0.035-0.012/-0.034-0.036/-0.071-0.120/-0.207-0.072/-0.1260/-0.0540/-0.087
>120–1800/-0.0180/-0.0250/-0.040-0.014/-0.039-0.043/-0.083-0.145/-0.245-0.085/-0.1480/-0.0630/-0.100
>180–2500/-0.0200/-0.0290/-0.046-0.015/-0.044-0.050/-0.096-0.170/-0.285-0.100/-0.1720/-0.0720/-0.115

Format: upper / lower deviation (mm). h6 / h7 — the fits most used for bearing and support-unit seats; g6 — clearance fit with relative rotation (sliding coupling end); f7 — clearance fit where running accuracy matters; d9 — large clearance for heat dissipation / sliding; e8 — medium clearance fit.

2. Parallel-key keyway dimensions and tolerances (GB/T 1095-2003)

Shaft dia d (mm)Key b × hShaft groove depth t1Hub groove depth t2Groove width H9Groove width N9Groove width P9Depth tol.Corner r
>8–103×31.81.40/+0.025-0.004/-0.029-0.006/-0.031+0.1/00.08–0.16
>10–124×42.51.80/+0.0300/-0.030-0.012/-0.042+0.1/00.16–0.25
>12–175×53.02.30/+0.0300/-0.030-0.012/-0.042+0.1/00.16–0.25
>17–226×63.52.80/+0.0300/-0.030-0.012/-0.042+0.1/00.16–0.25
>22–308×74.03.30/+0.0360/-0.036-0.015/-0.051+0.2/00.25–0.40
>30–3810×85.03.30/+0.0360/-0.036-0.015/-0.051+0.2/00.25–0.40
>38–4412×85.03.30/+0.0430/-0.043-0.018/-0.061+0.2/00.25–0.40
>44–5014×95.53.80/+0.0430/-0.043-0.018/-0.061+0.2/00.25–0.40
>50–5816×106.04.30/+0.0430/-0.043-0.018/-0.061+0.2/00.25–0.40
>58–6518×117.04.40/+0.0430/-0.043-0.018/-0.061+0.2/00.25–0.40
>65–7520×127.54.90/+0.0520/-0.052-0.022/-0.074+0.2/00.40–0.60
>75–8522×149.05.40/+0.0520/-0.052-0.022/-0.074+0.2/00.40–0.60

Shaft groove width: H9 loose / N9 normal (most common) / P9 tight. Shaft groove depth is dimensioned as d − t1 with a negative deviation; pick the smaller corner radius r that your cutter and stress level allow.

3. Circlip (retaining ring) groove dimensions (GB/T 894-2017, type A)

Shaft dia d0 (mm)Ring sizeGroove dia d2 (mm)Groove dia tol.Groove width m (mm)Groove width tol.Edge distance n ≥ (mm)Clearance d4 ≥ (mm)
10Ring 109.60/-0.111.1+0.14/00.617.0
12Ring 1211.50/-0.111.1+0.14/00.819.0
15Ring 1514.30/-0.111.1+0.14/01.122.6
17Ring 1716.20/-0.111.1+0.14/01.225.0
20Ring 2019.00/-0.131.3+0.14/01.528.4
22Ring 2221.00/-0.131.3+0.14/01.530.8
25Ring 2523.90/-0.211.3+0.14/01.734.2
28Ring 2826.60/-0.211.6+0.14/02.137.9
30Ring 3028.60/-0.211.6+0.14/02.140.5
35Ring 3533.00/-0.251.6+0.14/03.046.8
40Ring 4037.50/-0.251.85+0.14/03.852.6
45Ring 4542.50/-0.251.85+0.14/03.859.4
50Ring 5047.00/-0.252.15+0.14/04.564
55Ring 5552.00/-0.302.15+0.14/04.570.4
60Ring 6057.00/-0.302.15+0.14/04.575.8
65Ring 6562.00/-0.302.65+0.14/04.581.5
70Ring 7067.00/-0.302.65+0.14/04.587.2
80Ring 8076.50/-0.352.65+0.14/05.398.2

Circlip material 65Mn, heat treated to HRC 44–51; groove-bottom fillet ≤ 0.5 mm; n is the edge distance from groove to end face; groove depth t = (d1 − d2)/2; d4 is the required clearance (bore). Values marked ≈ in the source are extrapolated per the standard.

4. Shaft-end locknut thread dimensions and tolerances (GB/T 197-2018 / GB/T 9160.2)

Screw shaft dia (mm)Lock threadPitch (mm)External 6g major diaExternal 6g pitch diaMatching locknutNut O.D. Dk (mm)
4–6M6×0.750.75-0.022 / -0.162-0.022 / -0.122Precision locknut / custom made–14
6–8M8×11.0-0.026 / -0.206-0.026 / -0.139Precision locknut / custom made–16
8–10M10×11.0-0.026 / -0.206-0.026 / -0.139No standard KM (KM0 = M10×0.75) — custom required18
10–12M12×11.0-0.026 / -0.206-0.026 / -0.144KM1 (M12×1)22
12–15M15×11.0-0.026 / -0.206-0.026 / -0.144KM2 (M15×1)25
15–17M17×11.0-0.026 / -0.206-0.026 / -0.144KM3 (M17×1)28
17–20M20×11.0-0.026 / -0.206-0.026 / -0.144KM4 (M20×1)32
20–25M25×1.51.5-0.032 / -0.268-0.032 / -0.182KM5 (M25×1.5)38
25–30M30×1.51.5-0.032 / -0.268-0.032 / -0.182KM6 (M30×1.5)45
30–35M35×1.51.5-0.032 / -0.268-0.032 / -0.182KM7 (M35×1.5)52
35–40M40×1.51.5-0.032 / -0.268-0.032 / -0.182KM8 (M40×1.5)58
40–50M50×1.51.5-0.038 / -0.318-0.038 / -0.218*M50×1.570
50–60M60×22.0-0.038 / -0.318-0.038 / -0.218*GB/T 812 round nut M60×2 (= KM12)85

External thread tolerance zone 6g, nut internal thread 6H. The KM series are precision locknuts dedicated to ball screws, with fixed pitches: KM0 = M10×0.75, KM1 = M12×1, KM2 = M15×1, KM3 = M17×1, KM4 = M20×1, KM5 = M25×1.5, KM6 = M30×1.5, KM7 = M35×1.5, KM8 = M40×1.5. Pitch diameters marked * are calculated per GB/T 197-2018.

5. Shaft-end spanner flats (reference dimensions)

Shaft dia d (mm)Across flats S (mm)Flat depth (centre to face)Flat length L (mm)Across-flats tol.Application
1084.010–12h12(0/-0.15)Small screws
12105.012–15h12(0/-0.18)Small screws
15126.015–18h12(0/-0.18)Small / medium
17147.015–20h12(0/-0.18)Small / medium
20168.018–22h12(0/-0.21)Medium
252010.020–25h12(0/-0.21)Medium
302412.025–30h12(0/-0.25)Medium / large
352814.028–35h12(0/-0.25)Medium / large
403216.030–40h12(0/-0.25)Large
453618.035–45h12(0/-0.28)Large
504020.040–50h12(0/-0.28)Large
604824.045–55h12(0/-0.30)Heavy duty

No dedicated national standard — these are industry reference values and the drawing governs. Flat symmetry ≤ 0.1 mm; parallelism of opposite flats ≤ 0.05 mm.

6. Surface roughness requirements (GB/T 1031-2009)

Machined areaRa (μm)ProcessNote
Ball raceway (thread surface)0.4–0.8grinding + lapping / polishingCore working surface — affects service life and noise
Support journal (bearing seat)0.8precision grindingMates with the bearing inner ring
Mounting journal (coupling / nut housing)1.6precision grinding / fine turningGeneral mating surface
Keyway side faces1.6–3.2fine milling / grindingWorking faces of the key
Keyway bottom3.2–6.3millingNon-working surface
Shaft shoulder face (locating face)1.6precision grindingLocating face for bearing / parts
Circlip groove side / bottom3.2–6.3turningNon-mating surface
Locknut thread surface1.6–3.2turning / grindingThread working surface
Centre hole1.6lappingMachining datum — must be protected
Non-mating outer diameter3.2–6.3turningGeneral surface

Preferred Ra series: 0.4 / 0.8 / 1.6 / 3.2 / 6.3 / 12.5… The raceway is the core working surface at 0.4–0.8 μm; support journals are ground to 0.8 μm for correct bearing inner-ring fit.

7. Runout inspection limits (GB/T 17587.3) — C5 ground / C7 rolled

Inspection itemLocationC5 ground (μm)C7 rolled (μm)Key note
E5 O.D. runoutScrew O.D. (per l5 segment)3240For high L/D ratio use the full-length table
E6.1 Support journal runoutSupport journal20–3240–63Critical for bearing fit accuracy
E7.1 Mounting journal runoutMounting journal8–1212–20★ Strictest — key control point
E8.1 Shoulder face runoutShaft shoulder face5–66–8Critical for axial locating
E9 Nut face runoutNut mounting face16–2520–32For preloaded nuts
E10 Nut O.D. runoutNut mounting diameter16–2520–32For rotating nuts
E11 Nut parallelismRectangular nut / 100 mm2532For flanged nuts

Reference values (industry practice); GB/T 17587.3-2017 gives limits by nominal diameter / length bracket, and the 2017 edition splits E6 / E7 / E8 into E6.1 / E7.1 / E8.1. E7.1 journal runout is the strictest and the main control point for assembly accuracy.

8. Coaxiality / circular runout tolerance values (GB/T 1184-1996)

Tolerance grade≤1>1–3>3–6>6–10>10–18>18–30>30–50>50–120>120–250>250–500>500–800
10.40.40.50.60.811.21.522.53
20.60.60.811.21.522.5345
3111.21.522.534568
41.51.522.5345681012
52.52.53456810121520
644568101215202530
76681012152025304050
81010121520253040506080
91520253040506080100120150
102540506080100120150200250300
11406080100120150200250300400500

Values in μm; select the column by datum feature diameter (use the larger cylinder). Untoleranced coaxiality follows the GB/T 1184 circular-runout general tolerance: H = 0.1 mm / K = 0.2 mm (default, note GB/T 1184-K on the drawing) / L = 0.5 mm.

9. General tolerances for linear dimensions (GB/T 1804-2000)

Tolerance grade0.5–3>3–6>6–30>30–120>120–400>400–1000>1000–2000>2000–4000
Precision f±0.05±0.05±0.1±0.15±0.2±0.3±0.5—
Medium m±0.1±0.1±0.2±0.3±0.5±0.8±1.2±2
Coarse c±0.2±0.3±0.5±0.8±1.2±2±3±4
Very coarse v—±0.5±1±1.5±2.5±4±6±8

Ball-screw machining normally uses grade m (medium); note it on the drawing as GB/T 1804-m. Step lengths, relief-groove positions and any other linear dimension without its own tolerance follow this table.

10. General tolerances for straightness and flatness (GB/T 1184-1996 / ISO 2768-2)

Tolerance grade≤10>10–30>30–100>100–300>300–1000>1000–3000
H (precision)0.020.050.10.20.30.4
K (medium)0.050.10.20.40.60.8
L (coarse)0.10.20.40.81.21.6

Where the drawing is silent, grade K (medium) applies — note it as GB/T 1184-K.

Frequently asked questions

Which tolerance zone should I use for a ball-screw shaft diameter?
Support journals that take a bearing inner ring default to h6 (h7 is acceptable above 30 mm, but check bearing clearance). Mounting journals for couplings or nut housings default to h7. Use g6 where the coupling end must slide. If in doubt, call up h6 / h7 from the table above — we re-check every drawing.
Which standard governs keyways?
Parallel-key keyways on shafts follow GB/T 1095-2003. Shaft groove width is normally N9 (normal fit); use H9 for a loose fit and P9 for a tight one. Dimension shaft groove depth as d − t1 with a negative deviation, and hub groove depth as d + t2.
How deep should a circlip groove be?
Groove depth t = (d1 − d2)/2, with d2 from the table above. On a 20 mm shaft: groove diameter d2 = 19.0 mm (0/−0.13), width m = 1.3 mm (+0.14/0), bottom fillet ≤ 0.5 mm, and at least 1.5 mm of edge distance to the end face.
How do I choose the shaft-end locknut thread?
Read the table by screw shaft diameter: a 12 mm shaft takes M12×1 (KM1 nut), 20 mm takes M20×1 (KM4), 30 mm takes M30×1.5 (KM6), and above 50 mm a GB/T 812 round nut is usual. External threads are 6g, mating internal threads 6H.
Is there a standard for spanner flats and centre holes?
Spanner flats have no dedicated national standard — the table above is industry practice and the drawing governs; hold symmetry to ≤ 0.1 mm. Centre holes are selected per GB/T 145, must be protected after machining, and call for Ra 1.6 μm.
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Tolerance values quoted from GB/T 1800.1-2020, GB/T 1095-2003, GB/T 894-2017, GB/T 197-2018, GB/T 9160.2, GB/T 1031-2009, GB/T 17587.3-2017, GB/T 1184-1996 and GB/T 1804-2000. Where a drawing specifies otherwise, the drawing governs.

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