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Comparison · Shaft–hub connection

Taper-Lock vs. QD bushings vs. keyless locking assemblies: which shaft–hub connection?

There are three well-trodden ways to fix a pulley, sprocket or gear to a shaft: the European Taper-Lock (TB) bushing, the American QD bushing, and the keyless locking assembly. All three transmit torque; they differ in how the torque gets there, whether there is backlash, whether the shaft needs a keyway, and how easily the part comes off again. Here they are, compared dimension by dimension.

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Comparison · Published 2026-09-12 · Wolfer Transmission

What the three designs are

A Taper-Lock (TB) bushing is a split, tapered sleeve. Grub screws draw it into the matching taper bore of the hub, the sleeve closes onto the shaft, and torque is transmitted through a keyway. It sits flush with the hub face, the 1008–5050 series covers Ø10–300 mm bores, and it is the most common quick-mount on pulleys and sprockets worldwide; to remove it you move a screw to the jacking hole and push.

A QD bushing is the American (SD-25) design: a sleeve with a flange, pulled into the hub taper by pull-up bolts from either side. The JA / SH / SDS / SD / SK / SF series are mostly inch-dimensioned and also transmit torque through a keyway. The flange allows mounting from either face and faster release, at the cost of the flange thickness in axial length.

A keyless locking assembly (R series) consists of inner and outer tapered rings and a ring of axial screws. Tightening the screws presses the tapers together: the inner ring clamps the shaft, the outer ring expands against the hub bore, and torque is carried by friction over the whole contact face — no keyway. Made to the GB 10071 / DIN 7190 patterns, common bores Ø6–200 mm, larger sizes to drawing.

Torque path and backlash

In TB and QD bushings the key carries the torque; the taper grip locates and assists. A key always has clearance in its keyway, and under reversing load that clearance is taken up in both directions — backlash and fretting follow. Fans, pumps and conveyors running in one direction do not care; servo positioning axes and drives that reverse often care a great deal.

A locking assembly has no key: torque is carried by the clamped contact over the whole bore, so it is backlash-free in both directions, and the shaft has no keyway notch to start a fatigue crack — which is why it holds up under shock, as in the ceramic-press application that ran three years without a failure. Capacity depends on bore size, type and screw class: a Ø50 mm shrink sleeve carries about 3,000 N·m and a Ø100 mm shrink disc about 30,000 N·m; each type's ratings are on its selector page.

The three shaft–hub connections compared
CriterionTaper-Lock (TB) bushingsQD bushingKeyless Locking Devices
ConstructionSplit tapered sleeve + grub screws, flush with the hubFlanged tapered sleeve + pull-up boltsInner / outer tapered rings + axial screws
Torque pathKeyway, taper friction assistsKeyway, taper friction assistsFriction over the full contact face, keyless
BacklashYes (key clearance)Yes (key clearance)Zero, both directions
Shaft preparationStandard keywayStandard keywayNo keyway; shaft h8 / bore H8
Mounting sideFrom one hub faceEither sideEither side
RemovalScrew moved to jacking holePull-up bolt moved to jacking holeLoosen screws, slide or remove
Radial / axial spaceMost compactCompact radially, plus flange lengthSomewhat larger radially; length by type
Typical usePulleys, sprockets, fans, pumpsFrequent wheel changes, restricted accessServo, reversing, shock loads, hollow shafts
Wolfer standard range1008–5050, Ø10–300 mmJA / SH / SDS / SD / SK / SF …R series, common Ø6–200 mm
Stock / lead timeCommon sizes in stock, same-weekCommon sizes in stock, same-weekCommon GB / DIN sizes in stock; custom 15–25 days

Bushing capacity is limited by the key; locking-assembly capacity by the transmissible torque Mt in its size table. The actual values are on the respective selector pages.

Mounting, space and shaft preparation

The TB bushing is the most compact but needs access to the hub face to reach the grub screws; the QD flange takes its bolts from either side, which helps where both faces are obstructed or the wheel is changed often. Both need a standard keyway cut in the shaft, with the shaft diameter chosen from the bushing's bore series — one bushing series fits many shaft sizes.

A locking assembly needs no keyway: machine the shaft to h8 and the hub bore to H8. At installation the shaft and bore must be clean and free of oil, and the screws are tightened in a diagonal sequence in several passes to the specified torque — never in one pass. Loosen the screws and the hub slides or comes off; it can be reused many times without losing capacity. It is somewhat larger radially than a bushing, and its length depends on the type (slim and short types are available).

Choosing by drive type

V-belt pulleys, timing pulleys and sprockets on motors, fans and pumps: a Taper-Lock bushing first — common sizes are in stock and ship the same week. Wheels that are changed frequently, or mounted where neither face is easy to reach: a QD bushing. Servo and positioning axes, frequent reversal, heavy shock loads, or shafts that must not be keyed: a locking assembly, with an external shrink disc on gearbox hollow-shaft outputs. Non-standard bores, keyways and outer profiles in all three lines are machined to drawing in 15–25 days.

FAQ

Common questions on this topic

Can a taper bushing replace a locking assembly?

For one-directional, continuous drives that are not sensitive to backlash — yes, and it is cheaper. For servo positioning, frequent reversal or heavy shock loads we advise against it, because the key clearance introduces backlash and fretting. The reverse substitution always works, at the cost of a slightly larger radial size and a higher price.

Are Taper-Lock and QD bushings interchangeable?

No. The taper angles, hub bores and screw layouts differ, so each must be paired with a pulley or sprocket bored for that pattern. Wolfer machines to the established TB and QD dimensional patterns, so our parts interchange with same-size branded parts — but TB and QD never interchange with each other.

What shaft preparation does a locking assembly need?

No keyway. Machine the shaft to h8 and the hub bore to H8, clean and free of oil and burrs. Tighten the screws in a diagonal sequence in several passes to the specified torque; a printed installation guide ships with every lot.

What are the lead times for the three connections?

Common TB / QD sizes and common GB / DIN locking-assembly sizes are stocked in Foshan and ship the same week. Non-standard bores, keyways, tapers or outer profiles are machined from solid to drawing, typically in 15–25 days. Pulleys and sprockets can be shipped already bored, keyed and bushed.

Related reading

Taper Bushings Locking Assemblies Taper-Lock (TB) Bushings QD Bushings

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