Ball Spline Selection Guide — Torque, Preload P0/P1/P2 & Series

A ball spline transmits rotary motion and torque while allowing linear movement along the spline shaft. This guide covers structure (flange SLF / tube SLT), torque rating, preload classes P0/P1/P2, the torque-life formula, and the SLF/SLT series.

1. Ball spline selection in 5 steps

Define the torque. Work out the maximum torque T (N·m or kgf·mm) including starting, peak and inertia load. The torque rating is the key number on the datasheet (the datasheets list dynamic Ca / static Coa in kgf and the allowable torque derived from them).
Define the stroke and speed. Required travel (mm) and rotational speed (rpm) set the shaft length and the groove lead I.
Define accuracy & preload. Pick the structure (flange / tube / roller) and the preload class. Ball-spline preload uses P0 / P1 / P2 — a different system from ball-screw preload (ZF/Z0/Z1/Z2/Z3). P0 = clearance / no preload, P1 = light preload, P2 = heavy preload.
Check the environment. Dust, coolant, clean-room duty decide sealing and material.
Match support & hub. Choose the fixed (BK) + supported (BF) ends by shaft diameter and verify the bearing fit.

2. Core formulas

Rated torque life (revolutions):

L = (Ca / P)^3 × 10^6 revolutions

where Ca is the dynamic rating and P the equivalent torque load. Convert to hours: Lh = L × 10^6 / (60 × rpm). For a life target (e.g. 20,000 h) solve for the required Ca.

Allowable torque vs shaft size: larger shaft diameter d and more ball turns raise both dynamic Ca and static Coa. The SLF/SLT tables below show the trade-off across shaft sizes.

Rigidity: axial/rotational rigidity (kgf/µm) rises with preload; a preloaded spline is stiffer but has higher friction torque. Keep within the DN-type limit for the groove lead and speed.

3. Structure & series

Type	Code	Characteristic	Typical use
Flange type	SLF	Flange-mounted outer race, easy to bolt to a housing; 40° gothic-arc groove	Robot joints, indexing, automation
Tube type	SLT	Thin-wall outer race, light and compact	Semiconductor, medical, compact mechanisms

SLF (flange) and SLT (tube) are the two structural families of the MOSIONX ball-spline line.

4. Catalog data — SLF / SLT dimensions & ratings

The tables below are the core MOSIONX catalog parameters for the SLF (flange) and SLT (tube) ball splines. All dimensions in mm; loads in kgf and kgf·m. The nominal size is the spline shaft outer diameter ØD (h7).

4.1 Model number coding

Matched type (the factory cuts the spline shaft and assembles the spline nut to order; assembly accuracy reaches precision class):

SLF 006 T2 N N S - 500 - P0 - B2 + N3 N3

Pos.	Meaning	Code / note
1	Spline nut	SLF: flange type / SLT: cylindrical (tube) type
2	Nominal shaft diameter	mm (006=6 … 050=50)
3	Ball rows	T2: two rows / T4: four rows
4	Flange shape	N: full-round (omit when there is no flange)
5	Spline shaft type	S: solid / H: hollow
6	Spline shaft length	mm
7	Shaft accuracy	N: normal grade / P: precision grade
8	Preload class	P0: no preload (omit for a single nut) / P1: light / P2: medium
9	Number of nuts	e.g. B2: two nuts on one shaft
10	Nut surface treatment	S standard / B1 black oxide / N1 chrome plating / P phosphate / N3 electroless nickel / N4 cold plating / N5 black chrome
11	Shaft surface treatment	same codes as position 10

· Omit the treatment codes when neither the nut nor the shaft has a surface treatment. Single-out type: spline shaft and nut can be supplied separately, so customers can stock and assemble them by themselves; the coding is simpler — SLF 006 T2 N + N3

4.2 Spline shaft cross-section (solid / hollow)

Table 3.1.1 — standard solid spline shaft cross-section (mm):

Nominal diameter	6	8	10	13	16	20	25	30	40	50
Minor diameter Ød	5.25	7.27	8.97	11.82	14.72	18.63	23.43	28.53	37.3	47.05
Outer diameter ØD h7	6	8	10	13	16	20	25	30	40	50
Weight (kg/m)	0.22	0.39	0.60	1.03	1.56	2.44	3.80	5.49	9.69	15.19
Ball diameter	1.5	1.5	2.381	2.778	2.778	3.175	3.5	3.5	6.35	7.144
Outer dia. tolerance (µm)	0 / -15	0 / -15	0 / -18	0 / -18	0 / -18	0 / -21	0 / -21	0 / -25	0 / -25	0 / -30

Table 3.1.2 — standard hollow spline shaft cross-section (mm):

Nominal diameter	6	8	10	13	16	20	25	30	40	50
Minor diameter Ød	2	3	4	7	8	10	15	16	20	26
Outer diameter ØD h7	6	8	10	13	16	20	25	30	40	50
Weight (kg/m)	0.177	0.33	0.506	0.872	1.25	1.82	2.92	3.93	6.75	11.4
Ball diameter	1.5	1.5	2.381	2.778	2.778	3.175	3.5	3.5	6.35	7.144
Outer dia. tolerance (µm)	0 / -15	0 / -15	0 / -18	0 / -18	0 / -18	0 / -21	0 / -21	0 / -25	0 / -25	0 / -30

4.3 SLF series dimensions

Model	Shaft dia. d (h7)	Ball rows	D	L	A	B	F	Oil hole Q	W	X	Y	Z
SLF006	6	2	14	25	30	6	7.5	1	22	3.4	6.5	3.5
SLF008	8	2	16	27	32	8	7.5	1.5	24	3.4	6.5	4.5
SLF010	10	2	21	33	42	9	10.5	1.5	32	4.5	8	4
SLF013	13	2	24	36	44	9	11	1.5	33	4.5	8	4.5
SLF016	16	2	31	50	51	10	18	2	40	4.5	8	6
SLF020	20	2	35	56	58	10	18	2	45	5.5	9.5	5.4
SLF025	25	4	42	71	65	13	26.5	3	52	5.5	9.5	8
SLF030	30	4	47	80	75	13	30	3	60	6.6	11	8
SLF040	40	4	64	100	100	18	36	4	82	9	14	12
SLF050	50	4	80	125	124	20	46.5	4	102	11	17.5	12

4.4 SLT series dimensions

Model	Shaft dia. d (h7)	Ball rows	D	L	S	L1	Oil hole Q	b (H8)	t (+0.05/0)
SLT006	6	2	14	25	16.7	10.5	1	2.5	1.2
SLT008	8	2	16	27	15.7	10.5	1.5	2.5	1.2
SLT010	10	2	21	33	20	13	1.5	3	1.5
SLT013	13	2	24	36	23	15	1.5	3	1.5
SLT016	16	2	31	50	34	17.5	2	3.5	2
SLT020	20	2	35	56	39.7	29	2	4	2.5
SLT025	25	4	42	71	50.3	36	3	4	2.5
SLT030	30	4	47	80	60	42	3	4	2.5
SLT040	40	4	64	100	70	52	4	6	3.5
SLT050	50	4	80	125	91	58	4	8	4

4.5 SLF series ratings

Model	C kgf	C0 kgf	CT kgf·m	C0T kgf·m	MA1 kgf·m	MA2 kgf·m	Nut g	Shaft kg/m
SLF006	137	225	0.46	0.76	0.39	3.48	36.7	0.22
SLF008	137	225	0.60	0.99	0.39	3.82	47	0.39
SLF010	285	397	1.62	2.25	0.95	8.53	100	0.60
SLF013	396	540	2.89	3.94	1.50	12.46	117	1.03
SLF016	545	849	4.77	7.43	3.71	26.09	226	1.56
SLF020	724	1109	7.90	12.09	5.53	38.00	303	2.44
SLF025	1003	1593	21.99	43.01	10.35	68.59	458	3.80
SLF030	1160	1980	30.26	62.93	15.68	93.27	633	5.49
SLF040	2972	4033	105.37	176.05	36.59	246.34	1430	9.69
SLF050	4086	5615	179.89	304.35	51.58	428.72	2756	15.19

4.6 SLT series ratings

Model	C kgf	C0 kgf	CT kgf·m	C0T kgf·m	MA1 kgf·m	MA2 kgf·m	Nut g	Shaft kg/m
SLT006	137	225	0.46	0.76	0.39	3.48	14	0.22
SLT008	137	225	0.60	0.99	0.39	3.82	16	0.39
SLT010	285	397	1.62	2.25	0.95	8.53	37	0.60
SLT013	396	540	2.89	3.94	1.50	12.46	52	1.03
SLT016	545	849	4.77	7.43	3.71	26.09	130	1.56
SLT020	724	1109	7.90	12.09	5.53	38.00	188	2.44
SLT025	1003	1593	21.99	43.01	10.35	68.59	285	3.80
SLT030	1160	1960	30.26	62.93	15.68	93.27	395	5.49
SLT040	2972	4033	105.37	176.05	36.59	264.34	843	9.69
SLT050	4086	5615	179.89	304.35	51.58	428.72	1758	15.19

C / C0: basic dynamic / static load rating; CT / C0T: basic dynamic / static torque rating; MA1 / MA2: allowable static moment. At the same nominal size the dynamic ratings of SLF and SLT are identical — the difference lies in nut structure and weight. Combine with the torque-life formula L=(Ca/P)³×10⁶ revolutions in section 2. Source: MOSIONX catalog pp. 184–191; full data subject to the original manufacturer's catalog. In stock at Shiyi Automation, cut-to-length and surface treatments available.

5. Preload classes P0 / P1 / P2

Ball splines use a two-point (or multi-point) contact preload expressed as P0 / P1 / P2:

P0 — clearance / no preload: lowest friction, for free linear sliding with light torque.
P1 — light preload: reduces backlash, medium stiffness, general automation.
P2 — heavy preload: highest stiffness and zero-backlash torque transfer, for heavy-duty indexing and servo joints.

Do not confuse this with ball-screw / linear-guide preload (ZF/Z0/Z1/Z2/Z3). They are separate systems — applying the screw classes to a spline is a common spec error.

6. Online selector

Use the selector to filter by shaft diameter, structure and preload, then open the CAD / 3D drawing for the exact model.

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7. Related technical guides

Dig deeper into precision grades, preload and the ball-screw / linear-guide families:

Precision Grades Preload & Interchange Ball Screws Linear Guides Support Units All Ball Spline Guides