Nahshon Technical Column #04 | Selection Guide

Specifying a ball screw is rarely the hard part of machine building — sourcing it is. Custom screws mean drawings, quotations and lead times measured in months; a worn screw on a production line means costly downtime while you wait; small-lot purchases often hit minimum order quantities. NSK's Compact FA series is the standardized answer: the most common shaft diameters, leads and lengths for factory automation are kept as catalog standard items in stock, in three models — PSS, USS and FSS. Pick the model, order from the table, and delivery is counted in days.

The three models at a glance

ItemPSS (General)USS (High-accuracy / Cleanroom)FSS (Transfer)
Accuracy grade (JIS)C5C3Ct7
Axial playDia. 6/8: 0.005 mm max.
Dia. 10+: 0 (oversize-ball preload)		0 (zero backlash)0.010 mm max.
Shaft diameter6–25 mm10 / 12 / 15 mm12 / 15 / 20 / 25 mm
Lead5–60 mm (by diameter)5 mm10 / 20 / 25 mm
Length rangeStroke 50–2 000 mmStroke 100–600 mmOverall 400–1 450 mm (cuttable)
LubricationStandard greaseLG2 low-dust greaseStandard grease
Typical useSemiconductor/LCD equipment, handling, measuring, medicalCleanroom semiconductor/LCD/inspection equipmentTransfer mechanisms

All three share the same compact platform: ball-nut outside diameter up to 30% smaller than the existing FA model, an end-deflector recirculation system allowing 5 000 min⁻¹ maximum speed with about 6 dB(A) lower noise than tube-type recirculation, a thin seal and an M5×0.8 grease fitting as standard on shaft diameters 10–25 mm (6/8 mm shafts are unsealed), and a service temperature limit of 80 °C.

PSS — the general-purpose workhorse

JIS C5 accuracy; axial play 0.005 mm max. for 6/8 mm shafts and zero for 10 mm and above via oversize-ball preload. It offers the widest range of diameter/lead combinations (dia. 6–25 mm, leads 5–60 mm, strokes 50–2 000 mm), and shaft ends are pre-machined to match WBK low-profile support units — no extra design work after purchase.

USS — for cleanrooms and higher accuracy

JIS C3 accuracy with zero backlash. The key difference is lubrication: LG2 low-dust grease is standard, cutting dust emissions by 90% versus general lithium grease — roughly 1/100 of the existing FA model. Available in dia. 10/12/15 mm, 5 mm lead, strokes 100–600 mm, with cleanroom-spec support units.

FSS — for transfer equipment, cuttable to length

JIS Ct7 accuracy, axial play 0.010 mm max., dia. 12/15/20/25 mm, leads 10/20/25 mm, overall lengths 400–1 450 mm. Its signature feature: the simple-side support unit mounts directly on the screw thread outside diameter, so no corner cutting is needed — you can cut the shaft yourself to set the stroke (NSK also accepts cutting orders). After cutting, re-check the permissible speed as the smaller of the shaft's critical speed and 5 000 min⁻¹.

Why "standard stock" matters

Every screw and support unit in the catalog is a stock item — standardization traded for lead time. The reference number tells the whole story: PSS1505N1D0361 = PSS model, 15 mm shaft, 5 mm lead, NSK control number, 361 mm shaft length. If no standard length fits, there are three paths: cut an FSS shaft, order a made-to-order screw, or have the shaft ends custom machined.

Selection in five steps

  1. Positioning or transfer? Transfer → FSS.
  2. Environment: cleanroom / low-dust → USS; general → PSS.
  3. Shaft diameter and lead, from thrust and speed requirements.
  4. Length: stroke plus nut length and support margins, matched to the nearest standard length.
  5. Shaft ends: standard ends fit WBK support units with no machining; special interfaces go the custom route.

Nahshon is an NSK distributor in Taiwan: Compact FA-PSS stock items ship on short lead times, USS/FSS are available to order, and custom shaft-end machining is offered per drawing. Not sure which model fits? Try our AI selection assistant or send us an inquiry.

Specifications compiled from the NSK Compact FA catalog E3239. See also: Ball Screw Accuracy Grades C0–C10.