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

Quick answer

A replacement ball screw should not be quoted by overall length alone. Two screws with the same overall length can still differ in thread length, shoulders, bearing journals, coupling end, and working travel; the RFQ should include overall length, thread length, both end details, nut direction, mounting holes, and machine model.

Do not quote only by overall length

Overall length looks like the easiest dimension to measure on a replacement ball screw, but do not quote only by overall length.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.

FAQ

**Why can the part fail to fit even when overall length is the same?**

Because installation depends on bearing journals, shoulders, lock threads, coupling end, and nut housing. Even with the same overall length, one wrong end dimension can prevent bearing preload or coupling alignment.

Next step

Turn this guide into an RFQ

When the specification direction is clear, send the details below together with quantity, lead time, and packing requirements.

Include these details

Old-part overall length, thread length, diameter, lead, and nut style.
Full old-part photos, both end details, nut flange, and mounting-hole photos.
Machine use, whether it is a like-for-like replacement, quantity, and lead time.

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