Fixed End, Support End or Heavy-Duty Fixed End? Ball Screw Support Unit Selection Guide

Published:2026-08-08 23:30:00

Ball screw support-unit selection

Define the end function first, then choose the housing and bearing configuration

A standard fixed end, a support end and a heavy-duty fixed end are not interchangeable price grades. They perform different tasks in axial location, radial support, rigidity and mounting. Select the end-support arrangement first, then verify the interface, shaft diameter, load and accuracy.

Standard fixed end establishes the axial datumStandard support end supports the opposite end radiallyHeavy-duty fixed end increases axial capacity and rigidity

HZMotion ball screw fixed-end, support-end and heavy-duty support units — HZMotion ball screw support-unit range

01 / Functional roles

What do fixed, support and heavy-duty fixed ends do?

Axial location

Standard fixed end

The bearing set, locknut and housing establish the ball screw's axial datum and carry operating thrust. Standard versions commonly use DF-arranged angular-contact bearings. The same housing families may also offer economical E configurations or TAC configurations with 60-degree angular-contact thrust bearings.

Typical use: automation equipment, CNC feed axes and general precision-positioning mechanisms.

View standard fixed-end series

Radial support

Standard support end

Mounted at the opposite end, it provides radial support and improves rotational stability. It does not establish the same axial datum or preload as the fixed end. Thermal-expansion compensation depends on the complete machine structure, fits and screw-end design and must be checked against the drawing.

Typical use: paired with a standard fixed end in a fixed-supported arrangement.

View standard support-end series

High load and rigidity

Heavy-duty fixed end

These units use 60-degree angular-contact thrust bearings and high-preload configurations, with DF, DFD, DFF, QBC and QFC arrangements available by series. Their purpose is higher axial capacity and support rigidity, not merely a larger standard housing.

Typical use: heavy-cutting machine tools, high-load feed axes and fixed-fixed pre-tensioned systems.

View heavy-duty fixed-end series

02 / Support arrangement

The two ends are not selected independently

Fixed endLocation + axial load

Ball screw

Support endRadial support + stability

Fixed-supported

The most common arrangement for conventional equipment. The fixed end locates and carries thrust; the support end improves radial stability at the opposite end. It is straightforward to assemble and suits many medium-load, general-stroke feed mechanisms.

Fixed-fixed or pre-tensioned

Both ends provide high-rigidity support. A controlled pre-tension can improve axial rigidity and manage thermal growth. This arrangement demands better base accuracy, coaxiality, assembly control and thermal design and is commonly evaluated with heavy-duty fixed ends.

Important: fixed-fixed is not automatically better. Incorrect datums, coaxiality or pre-tension can impose extra bearing load and raise temperature. Review screw length, speed, thrust, heat generation and base accuracy together.

03 / HZMotion series pairing

Select the mounting interface first, then the bearing grade

Fixed-end series	Matching support end	Mounting interface	Shaft diameter range	Common configurations
EK	EF	Mounting face parallel to screw axis	5-25 mm	Standard, E, TAC
BK	BF	Mounting face parallel or perpendicular to screw axis	10-50 mm	Standard, E, TAC
FK / FKA	FF	Mounting face perpendicular to screw axis	6-30 mm	Standard, E, TAC on applicable families
AK	AF	Mounting face parallel to screw axis	10-25 mm	Standard, E
LK	LF / LFA	Mounting face parallel to screw axis	6-25 mm	Standard, E

This table narrows the range using the current HZMotion product-line summary. Final selection must use the detailed drawing for d1, bolt pattern, center height, thread and shoulder dimensions.

BK standard fixed-end unit components — A BK fixed end includes the housing, bearing set, holding lid, seals, locknut and collars.

BK fixed-end ball screw interface dimensions — A model number does not replace interface verification: check shaft, shoulder, thread and effective length.

How is a standard TAC configuration different from a heavy-duty fixed end?

BK-TAC, EK-TAC and FK-TAC place 60-degree angular-contact thrust bearings in familiar standard-housing interfaces, useful when increased axial capacity is needed without changing to a dedicated heavy-duty housing. SBK, SBK-U, WBK, FBSA and MBK form a dedicated heavy-duty line with higher load ranges, more bearing arrangements and fixed-fixed applications. Compare the interface, bearing count, arrangement, preload, accuracy and available space - not just one maximum-load value.

Heavy-duty series	Shaft diameter range	Mounting orientation	Typical considerations
SBK / SBK-U	25-40 mm	Mounting face parallel to screw axis	High axial rigidity, DF/DFD arrangements, heavy feed axes
WBK	17-40 mm	Mounting face perpendicular to screw axis	DF/DFD/DFF arrangements and fixed-fixed systems
FBSA	20-60 mm	Mounting face perpendicular to screw axis	Double- and four-row arrangements for larger screws
MBK	15-20 mm	Mounting face perpendicular to screw axis	Compact heavy-duty support with DF/DFF arrangements

04 / Selection process

Six steps for preliminary selection

Define the support arrangementChoose fixed-supported or fixed-fixed/pre-tensioned before selecting a product family.
Check the machined screw endVerify d1, shoulder location, thread, circlip groove, effective length and tolerances.
Check the machine mounting faceUse mounting-face orientation, center height and bolt pattern to choose EK, BK, FK, AK, LK or a heavy-duty family.
Calculate axial loadInclude acceleration thrust, cutting force, gravity, shock, duty cycle and a suitable safety margin.
Match accuracy and preloadUse the ball screw accuracy and positioning target to choose E, standard C5/C4, TAC5/TAC4 or heavy-duty C5/C4 configurations.
Review speed, heat and assemblyLong or high-speed axes also require critical-speed, temperature, coaxiality, base-rigidity, lubrication and protection checks.

Find support-unit models Support-unit life calculator Download manuals

05 / Common mistakes

Five details frequently missed

Selecting by screw diameter alone

The same screw diameter can use different end shafts, threads and spaces. Use the machined-end drawing.

Treating the support end as a cheaper fixed end

It does not provide the same axial locating and preload function and is not a substitute.

Comparing maximum axial load only

Also compare arrangement, preload, accuracy, interface, speed and system rigidity.

Disassembling a factory-set fixed end

Fixed ends are supplied with bearing preload adjusted and grease filled. Uncontrolled disassembly can disturb the preload.

Ignoring base accuracy and coaxiality

Unequal mounting heights, misalignment or forced assembly can create extra load and heat even when the product is correctly selected.

06 / Quick answers

Frequently asked questions

Does every machine need one fixed end and one support end?

It is the most common arrangement, but not the only one. Short strokes, cantilever layouts and fixed-fixed systems require a separate load, speed, rigidity and thermal review.

Does a TAC type eliminate the need for a heavy-duty fixed end?

Not necessarily. TAC increases axial capacity within common housing interfaces. Heavy-duty units add dedicated structures and more bearing arrangements. Compare thrust, rigidity, space and the complete support scheme.

Must fixed- and support-end model numbers have the same size number?

Do not decide from the number alone. BK and BF are paired families, for example, but each screw-end interface still needs to be checked separately against the product drawing.