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A ball screw's positioning accuracy depends on the whole end-support set—fixed side plus support side—not on buying one good bearing. The fixed side carries axial load and sets positioning rigidity; the support side lets the screw expand thermally without accumulating stress. The two ends play different roles, so they call for different selection logic. SYK's (Sonyung Industry Co., Ltd.) low-profile family—the LK fixed side paired with the LF/LFA support side—is the set built for machines that are space-constrained yet still need rigidity. This guide lays out how the two ends divide the work, how to pair them, and which specs to match, so you get the set right the first time.

The two ends of a screw are not two independent purchases—they are one system: the fixed side locks axial accuracy, the support side lets thermal expansion float. Get either end wrong and the whole screw's repeatability suffers.

SYK has produced ball screw support units under a single-facility, vertically integrated model since 1989, making the fixed side and support side on the same line, with a standard lead time of 1–3 working days and no minimum order quantity.

Why look at the whole end-support "set" instead of a single bearing?

You look at the whole end-support set because the two ends of a ball screw do different jobs: one is fixed, the other floats. The fixed side uses an angular-contact bearing to lock axial position and rigidity, while the support side uses a deep-groove ball bearing to carry radial load and simultaneously let the screw grow axially as temperature rises. This "one end fixed, one end supported" arrangement holds accuracy and thermal stability at the same time.

If both ends are fixed, the screw has nowhere to release its thermal growth, so stress builds up between bearing and screw—raising running resistance at best and shortening life at worst. Conversely, asking the support side to do the fixed side's job leaves axial rigidity too low, and positioning drifts. The correct approach is to let the fixed side take the axial load and the support side keep expansion headroom—two roles, neither optional.

That is why support units are best planned as a set. Decide which end is the driven, fixed end and which is the floating, supported end first, then map each to the right fixed-side and support-side model, so you never buy a combination that is redundant or under-specified.

What goes wrong if you pick only the fixed side and ignore the support side?

Picking only the fixed side and ignoring the support side leads to three common failures: thermal-stress buildup, build-height interference, and mismatched journal diameters. The support side looks like a supporting actor, but it directly decides whether the screw can expand freely and whether the whole set fits the mechanism—ignore it, and those problems surface on the assembly floor.

The first problem is thermal stress. Long-stroke or high-speed screws heat up and grow during operation; if the supported end has no expansion headroom, that growth turns into positioning error and added bearing load. The second problem is build height. If you specify a low-profile LK fixed side but a tall standard support unit, the mechanism still will not fit—low-profile only works as a matched set.

The third problem is the most practical: the two journal diameters differ. A screw's fixed end and support end are usually machined to different diameters, so the fixed side matches one bore and the support side matches another. Order only the fixed side, and the supported end may simply not fit. Planning both ends together avoids that on-arrival mismatch.

How does SYK's low-profile family divide the work—what do LK and LF/LFA each do?

SYK's low-profile family separates fixed side from support side by bearing type: the LK fixed side uses DF angular-contact preloaded bearings to lock axial accuracy, while the LF/LFA support side uses deep-groove ball bearings located by C-clips to allow axial float. Both are low-profile, both are made in-house, and pairing consistency is controlled by one process.

The LK fixed side spans bores of 8–15 mm (LK08/LK10/LK12/LK15), with bearings preloaded to zero axial clearance, compatible with C3–C10 screws, and responsible for axial load and positioning rigidity. The support side comes in two series: LF (LF08/LF12/LF15) and LFA (LFA12/LFA15/LFA20/LFA25), spanning bores of 6–25 mm, using deep-groove bearings (such as 606ZZ, 6000ZZ, 6801ZZ) located by C-clips, compatible with C3–C7 screws.

The two series differ structurally: LF is retained by a single C-clip, LFA by two C-clips locating from both sides, and their bearing sizes and bore ranges differ too. SYK builds the housings, bearings, clips, and seals for both the fixed and support sides on one vertically integrated line—so a low-profile end-support set is held to a single standard from the fixed end to the floating end.

What do you actually save by specifying both ends at once?

Specifying both ends at once saves three things: lead time, alignment hours, and batch variation. When the fixed side and support side come from the same vertically integrated factory, their surface finish, lead time, and quality standard match—so the design team aligns CAD once and purchasing chases a single order, and deployment speeds up noticeably.

There are three concrete benefits. First, matched lead time: SYK's standard items ship in 1–3 working days, custom in 5–7, with no MOQ, so both ends are ready together—no "fixed side arrived, support side still waiting" gap. Second, assembly repeatability: one in-house process keeps each set's body height, hole pattern, and bearing sealing standard consistent, so a new batch does not force re-calibration. Third, design alignment: both the fixed and support sides come with 2D/3D CAD, so engineers can fit both ends into the mechanical envelope at the design stage, backed by thrust, salt-spray, life, and axial-reciprocating testing.

In short: handing the whole set to one line saves not just a purchasing step, but the entire span of time from design alignment to production calibration.

How do you pair the fixed side and support side? LF/LFA specs at a glance

You pair the fixed side and support side by matching each end's journal: the fixed-end journal decides the LK model, the supported-end journal decides the LF or LFA model, and the two need not share a number. Because a screw's two ends are usually machined to different diameters, pairing follows each end's actual bore—not a matching of model-number digits.

The roles of the fixed side and support side compare as follows:

Select the support side by the supported-end journal using the LF/LFA specs below:

Application routing is direct too: for semiconductor, medical, and desktop automation machines—space-constrained and often cleanroom—choose an LK fixed side and an LF/LFA support side, and specify electroless nickel across the whole set; for general factory environments, black oxide across the set is enough. Keep the finish identical on both ends so a single screw never carries housings with different coatings.

Speccing a low-profile support set: remember these three steps

Speccing a low-profile support set takes three steps: fix the axial load first, then the supported-end journal, then the surface finish. Step one: choose the LK fixed-side bore (8–15 mm) by the screw's axial load and positioning needs. Step two: measure the supported-end journal and map it to an LF or LFA model (bore 6–25 mm). Step three: decide black oxide or electroless nickel for the whole set by operating environment.

If the screw spec is already set, give SYK four data points—fixed-end journal, supported-end journal, screw accuracy, and operating environment—and the factory will return a complete low-profile fixed-side plus support-side model set with lead time. Running from the fixed end to the floating end on one line is exactly why this pairing can balance space, rigidity, and short lead times.

Frequently Asked Questions (FAQ)

Q1: What is the difference between the fixed side and the support side—do I have to buy them as a set?

The fixed side carries axial load and sets positioning rigidity, using an angular-contact preloaded bearing; the support side carries radial load and allows thermal expansion, using a deep-groove ball bearing. Standard ball screws use a "one end fixed, one end supported" arrangement, so they are used as a set and the two roles are not interchangeable.

Q2: Why does the support side (LF/LFA) use a deep-groove ball bearing instead of angular contact?

The support side's job is radial support while letting the screw expand axially, and a deep-groove ball bearing allows exactly that float. If the supported end also used a fixed angular-contact bearing, the screw's thermal growth would have nowhere to go and stress would build up. Axial locking is the LK fixed side's job.

Q3: What is the difference between the LF and LFA series—which should I choose?

Both are low-profile support sides; they differ in retention structure and bore range. LF is retained by a single C-clip (bore 6–15 mm); LFA is located by two C-clips (bore 12–25 mm). Choose by the supported-end journal and locating needs, and if unsure, send the screw spec to the factory for a match.

Q4: Do the fixed side and support side have to use the same surface finish?

It is recommended. If one end of a screw is black oxide and the other electroless nickel, corrosion protection can be uneven in cleanrooms or humid environments. The rule is to specify by environment across the whole set: black oxide throughout for general environments, electroless nickel throughout for clean or anti-corrosion needs.

Q5: Which screw accuracy grades do the LF/LFA support sides fit?

The LF/LFA support sides fit C3–C7 screws, while the LK fixed side fits C3–C10. When the fixed and support sides are used as a set, plan the whole set to the stricter of the two ends.

Q6: What are the lead time and MOQ for a matched set—can I re-order just the support side?

SYK's standard lead time is 1–3 working days and custom is 5–7, with no minimum order quantity; you can order the full set or re-order the fixed or support side alone. When re-ordering just the support side, provide the screw's supported-end journal and your current fixed-side model so the factory can match it.

Contact SYK

For a matched low-profile fixed-side plus support-side recommendation (LK × LF/LFA), 2D/3D CAD files, or help confirming set lead time, contact SYK directly. Share the screw's fixed-end journal, supported-end journal, accuracy grade, and operating environment, and the factory will map the complete model set and lead time.