Why a Replacement Ball Screw Should Not Be Quoted Only by Overall Length

Do not quote only by overall length

Overall length looks like the easiest dimension to measure on a replacement ball screw, but do not quote only by overall length. Two screws can have the same overall length and still fail to fit because thread length, end lengths, bearing journals, and the coupling end are different.

Same overall length does not mean same installation dimensions

Machine installation depends on support units, bearings, lock nuts, coupling, and the nut housing. If a shoulder on the fixed side moves by 5 mm, or the support side end is 10 mm shorter, bearing preload or coupling position can be wrong.

Confirm thread length and working travel separately

Thread length affects the nut moving range, while working travel also depends on nut length, housing, limit positions, and safety distance at both ends. Overall length alone does not show whether the new part can cover the original travel.

End details decide whether the old supports fit

Measure end lengths, bearing journal diameters and lengths, lock threads, keyways, retaining grooves, and coupling end size separately. If the old part is worn, recheck diameter at an unworn position and photograph the measurement location.

Replacement RFQ checklist

Overall length, thread length, working travel, and both end lengths.
Bearing journals, shoulders, lock threads, and grooves on fixed and support sides.
Coupling end diameter, length, keyway, or flat requirement.
Nut direction, flange direction, mounting hole positions, machine model, and quantity.

Typical buyer situations

This topic usually appears in distributor stocking, repair replacement, machine retrofit, automation projects, and drawing-based purchasing. If a buyer sends only one model number, the supplier cannot judge the real use, packing risk, or whether machining upgrades are needed.

Details to confirm before quotation

To reduce repeated questions, the RFQ should cover product specification, use case, and delivery expectations together. The following points can be copied into the RFQ form or email.

Purchase purpose: distributor stock, repair replacement, machine project, or sample testing.
Specification: diameter, lead, overall length, thread length, nut type, and quantity.
Machining: cut-to-length, end machining, and whether BK/BF, FK/FF, EK/EF, or other supports must be matched.
Delivery: target quantity, expected lead time, packing, labels, shipping method, and whether shipment photos are required.

Common mistakes

A common mistake is asking only for unit price without application, quantity, or packing details. Another is sending photos without dimensions. This turns quotation into guesswork and can create errors in end machining, nut matching, or long-part shipping.

Next step

If the specification is clear, submit an RFQ directly. If the model or accuracy grade is still uncertain, describe the machine use and old part details so the supplier can recommend a standard part, bar stock, cut-to-length, or end machining route.