A ball spline is the only rolling-element bearing that transmits torque and linear force on a single shaft, and GlobalSpec's 2026-07-18 selection guide defines its core behavior: the bearing balls travel in a straight, non-helical path, giving near-friction-free linear motion while handling torsional load on the same shaft [S1].
For a linear motion stage, the RFQ must therefore fix the shaft outer diameter, the nut style, the ball material (most catalog parts are 440C stainless steel per MISUMI's standard ball spline listing [S4]), the basic dynamic load rating C, and the lubrication class. Treat the part like a ball bearing for life calculation and like a linear motion bearing for stroke and rigidity; it sits at the intersection of both.
Five Mandatory RFQ Fields and Why Each One Matters
An RFQ that omits any of the following five fields will be returned for clarification or quoted against defaults that inflate cost by 15-30%.
1) Shaft outer diameter D (mm). MISUMI's standard series catalogs D at 6, 8, 10.4, 13.4, and 16.6 mm with basic dynamic load ratings C scaling from 1200 N at D=6 mm to 6200 N at D=16.6 mm [S4]. Specifying D and a tolerance band (typical h6 or h7) is the single highest-leverage line on the RFQ because every downstream load and rigidity calculation keys off it.
2) Nut type. The four catalog options are Straight, Flanged, Compact Flange, and Round Flange [S3]. For a linear motion stage the Flanged or Round Flange style is the practical default; a Straight nut forces the machine builder to fixture the nut body, which adds assembly cost and misalignment risk.
3) Basic dynamic load rating C and basic static load rating C0. From the MISUMI table, D=10.4 mm yields C=2400 N and a rated stroke band of 60-400 mm [S4]. Always state C and C0 explicitly; do not let the supplier pick.
4) Ball material and shaft material. Standard 440C stainless steel balls run against a 440C stainless steel shaft is the catalog default [S4]. For semiconductor or medical cleanrooms step up to a vacuum/cleanroom grease, and for food or washdown specify a stainless-on-stainless pair with food-grade lubricant.
5) Stroke length and shaft end machining. The MISUMI configurable L-dimension part numbers (e.g. "Both Ends Tapped" code 110302368220, "Both Ends Stepped" code 110302209750) show that end-machining is a separate RFQ line [S5][S7]. Omit it and the supplier will assume raw-cut ends, which rarely fits a stage assembly.
Nut Series Compared: Standard, Medium Torque, and Separate-Nut Designs
Three nut families compete for the linear motion stage slot, and each one trades torque capacity against shaft inertia and ease of assembly. [S3]
Standard series (MISUMI code 110300024960) covers D=6-16.6 mm with C ranging 1200-6200 N and a maximum rated stroke of 70-400 mm depending on diameter [S4]. It is the lowest-cost, shortest-lead-time option and the right pick when torque demand is moderate and the stage runs a single nut on a fixed shaft.
Medium-torque rotary nut, LTR series (THK, distributed via MISUMI code 221000087965) is the upgrade path when the application needs higher torsional stiffness on the same shaft envelope [S6]. The LTR geometry re-circulates balls through a larger path, raising C without changing D; expect a 20-40% price premium over the standard series for the same D, and a longer lead time because THK-brand parts ship on a different stocking schedule than MISUMI-brand equivalents.
Separate-nut designs, IKO model LSAG (MISUMI code 221006227002), decouple the nut body from the load-carrying element so the nut can be installed or replaced without removing the shaft [S9]. Specify LSAG when the stage is a long-stroke assembly where shaft pull-through is impractical, or when the design needs a ball screw and a ball spline on the same shaft with a single nut swap point.
Load Cases, Torque Capacity, and Common Under-Spec Traps
Ball splines fail in three predictable modes, and each one traces to a specific RFQ omission. [S1]
Mode 1: torsional overload. GlobalSpec's guide states that ball splines transmit torque while providing linear motion, so the RFQ must state the application torque in N·m and check it against the catalog C_T (torsional load rating) [S1]. Buyers who specify only the linear load C and leave torque off the RFQ get a part that passes linear life calculation but gall at the ball-race interface under reversing torque.
Mode 2: stroke overrun. The MISUMI standard series is rated for strokes between 60 mm and 400 mm depending on D [S4]. A linear motion stage that needs 500 mm stroke on a D=10.4 mm shaft is outside the standard catalog and must be quoted as a special; the buyer who writes "stroke 500 mm" without flagging the catalog limit will wait for a custom quote while a competitor with a 16.6 mm shaft gets a catalog delivery.
Mode 3: lubrication starvation. Standard 440C stainless steel on 440C stainless steel ships with a factory rust-preventive oil, not a working lubricant [S4]. For any stage that runs more than a few cycles per shift, the RFQ must specify the lubrication class (Standard S2, long-life LG2, or food-grade ET-100K in the MISUMI naming convention [S4]); choosing the wrong class is the single most common cause of premature brinelling and is invisible at the quote stage.
Material, Lubrication, and Environmental Selections
440C stainless steel is the catalog default for both the balls and the shaft raceway in the MISUMI standard series [S4]. It gives Rc 58-60 hardness, corrosion resistance suitable for washdown, and compatibility with the three named lubrication grades (S2 standard, LG2 long-life, ET-100K food-grade) [S4].
For cleanroom or vacuum stages, push the RFQ to a low-outgassing grease and a 440C shaft with a special surface finish; for high-cycle production stages (more than 2,000 cycles per hour), specify LG2 long-life lubrication as a non-optional line because Standard S2 will reach grease exhaustion within 6-12 months under that duty. The MISUMI "L Dimension Configurable Type" part numbers (Standard S2, LG2, ET-100K) are the explicit hook to call this out per part number [S4].
Ceramic hybrids on a ball spline are rare in the catalog and trigger a custom-engineering path; the same life gain on a linear motion stage is usually cheaper to reach by stepping D up one size (for example, 10.4 mm to 13.4 mm) and staying in the standard 440C/440C material pair [S4].
End-Machining, Mounting, and Shaft Integration
The shaft end-machining is its own RFQ line because it determines how the spline shaft integrates with the stage end blocks, the encoder, and any motion controller mounting flange. [S1]
MISUMI offers Both Ends Tapped (code 110302368220) for through-bolt or stud retention, and Both Ends Stepped (code 110302209750) for shoulder-retained assemblies where axial location must be positive [S5][S7]. Tapped ends are the cheap default and work for most stage builds; stepped ends are required when the stage must resist axial thrust without a retaining ring, or when the same shaft carries a ball spline at one end and a ball screw at the other.
For stage builders integrating a rotary encoder on the protruding shaft end, the encoder-hub side usually wants a stepped and ground journal (h6 tolerance) rather than tapped ends, so specify the stepped configuration and a "shaft extension for encoder mounting" note on the RFQ. This is also the line that catches a common mistake: writing a tapped-end part number when the next assembly operation needs to press-fit a pulley or pinion; the supplier cannot rework tapped ends, and the order has to be re-placed.
RFQ Line Template and Sourcing Standards
A complete ball spline RFQ line for a linear motion stage should read, in this order: [S1]
Line 1: Function. "Linear motion stage, X-axis, stroke ___ mm, peak linear load ___ N, peak torque ___ N·m, cycles/hr ___, duty hours/day ___."
Line 2: Part. "Ball spline, ball spline, shaft OD D = ___ mm (h6 or h7), length ___ mm, end-machining: Both Ends Tapped / Both Ends Stepped [S5][S7]."
Line 3: Nut. "Nut type: Flanged / Round Flange / Compact Flange / Straight [S3]; basic dynamic load rating C ≥ ___ N; basic static load rating C0 ≥ ___ N."
Line 4: Material and lube. "Balls and race: 440C stainless steel [S4]; lubrication class: S2 / LG2 / ET-100K [S4]."
Line 5: Environment. "Ambient temperature ___ °C, atmosphere (cleanroom / washdown / vacuum / standard), IP rating target."
For US-bound builds, this is the tariff line that drives landed cost on catalog parts from Asian warehouses such as Made-in-China-listed THK VRU-series tables, which quote roughly US$20-90 per piece at 1-piece MOQ for cross-roller alternatives [S8]. Note that the THK VRU series is a cross-roller slide table, not a ball spline, and the two are not interchangeable on a linear motion stage RFQ even though both carry balls.
For a deeper spec-gate on related bearings used in the same stage, see Angular Contact Bearing Selection for Automotive Production Lines and Angular Contact Bearing Selection for Pulp and Paper: 2026 Spec Gate Map; for a broader part-selection map across an industrial facility, the embedded part selection spec map covers how a ball spline RFQ fits into a multi-component bill of materials.