What Is a Shaft Collar? Types and How They Hold
Short answer
- A shaft collar is a ring that clamps onto a shaft to create an adjustable shoulder, used as a mechanical stop, spacer, bearing retainer or locating ring.
- Set-screw, one-piece clamp, two-piece clamp and threaded types differ in how they grip: clamp styles spread load over the whole bore, while set screws dig into the shaft at one point and can leave a burr.
- Collars suit light-load stops and positioning, but they are not a coupling and should not be the only retention against a heavy or dynamic load.
A shaft collar is a ring that clamps onto a shaft to create an adjustable shoulder. It is used as a mechanical stop, a spacer, a bearing retainer or a locating ring, and it can be slid and re-fixed anywhere along the shaft without machining a groove.
What is a shaft collar for, and what is it not for?
A collar positions and limits. It stops a part from sliding along the shaft, sets a gap between two components or limits travel on a rod. It is not a coupling and it is not designed to transmit torque as a main function, although some types can carry modest torque by friction. If the job is to drive a wheel or gear, use a key, a bushing or a proper hub.
How does a set-screw collar hold, and what damage can it cause?
The simplest type is a solid ring with one or two set screws that bear on the shaft. Fast to fit, and they hold well against axial load in many general uses. Their drawback is damage. The screw tip digs into the shaft surface and raises a burr. Slide the collar along and the burr scores whatever is on the shaft, and the dimple left behind marks the position. On a ground linear shaft or a precision shaft, that is a real problem. A flat on the shaft, or a collar with a brass-tipped or nylon-tipped screw, reduces damage but also reduces holding force.
How does a one-piece clamp collar grip a shaft?
A solid ring is slit on one side and has a clamping screw across the slit. Tightening the screw squeezes the ring around the shaft. The clamp spreads the load over the whole bore instead of one point, so there is no burr and the shaft survives repeated adjustment. Holding power is generally higher than a set screw collar of the same size. Because the ring must be slid on from the shaft end, the one-piece style is unsuitable where the shaft ends are blocked by other components.
When should you use a two-piece clamp collar?
Two halves held together by screws. They can be fitted on a shaft in the middle of an assembly without removing anything, which makes them the usual pick for maintenance and for retrofits. The grip is even and the collar can be tightened and loosened many times. They tend to be bulkier and use more screws, so tightening evenly matters. Alternate between the screws and bring them up together.
What is a threaded shaft collar and when is it used?
These screw onto a threaded shaft or threaded rod, often with a locking feature such as a set screw or a slot for a lock nut. They give very fine axial adjustment and a strong stop. They need threaded shaft, which is not what every machine has.
What determines how much a shaft collar can hold?
A clamp-style collar works by friction between its bore and the shaft, so the more clamp force, the more it holds. A set-screw collar holds differently, by digging the screw tip into the shaft. Several things change this:
- Clamp screw torque. Under-tightened collars slip, and over-tightened ones can distort the bore or strip the screw. Use the torque the maker recommends.
- Shaft surface. Oil or a polished finish lowers friction. Clean the shaft and the bore before fitting.
- Shaft hardness. A hard shaft resists set-screw dig. It can also let a set screw slip.
- Direction and type of load. A steady push is easier on a collar than vibration or shock, which can walk a screw loose.
The maker's published figures give axial holding capacity for each size under defined conditions. Treat the figure as a guide for a clean, correctly tightened collar and leave a good margin for shock and vibration.
How should a shaft collar bore fit the shaft?
A collar bore is made slightly larger than the nominal shaft so that it slides on. Inch and metric bores are both common, and a metric collar on an inch shaft of nearly the same size may appear to fit while gripping badly. A loose bore reduces contact and holding power, and a clamp collar that closes up fully before it grips has the bore too large. Check the shaft diameter with a micrometer rather than assuming it from the nominal size.
How do you avoid shaft damage from collars?
On a precision shaft, never put a set screw directly on the running surface. Use clamp collars, or place a set-screw collar on a section of shaft that does not carry a bearing. Where a set-screw collar has to be moved, file the burr off before sliding it along. A collar that is put back on an old dimple will not seat the same way twice.
Is a shaft collar safe to use as a stop?
Collars work well as stops for light loads, such as limiting the travel of a sliding carriage on a rod or setting the position of a bearing. They are not safe as the only retention against a heavy or dynamic load. If a failure could cause a hazard, put in a proper shoulder, a retaining ring in a groove or another positive stop. A collar can also slip under impact, so do not rely on one to arrest a moving mass.
What do people commonly ask about shaft collars?
Which type is best for a linear shaft?
A clamp collar, either one-piece or two-piece. Set screws mark the shaft and the burr damages bushings and seals.
Can I reuse a collar?
Clamp collars are fine to reuse if the screw threads and the bore are undamaged. Set-screw collars lose some holding when the shaft is already dimpled.
What material should I choose?
Steel for strength and general use. Stainless where corrosion or washdown is an issue, and aluminum where weight matters and loads are low. Plastic collars suit light-duty or non-marking uses.
Further reading on this site: linear shafting and ball bushings; mounted bearing units; bearing shaft and housing fits; linear guide mounting and alignment; linear bushing vs profile rail; the KKM catalogue.
If you need a collar to match an existing one, give us the shaft diameter, collar width and style and we will help track down an equivalent.
Frequently asked questions
What is a shaft collar used for?
A shaft collar is a ring that clamps onto a shaft to create an adjustable shoulder. It works as a mechanical stop, a spacer, a bearing retainer or a locating ring, and it can be slid and re-fixed anywhere along the shaft without machining a groove. It positions and limits parts rather than transmitting torque as a main function, so a key, bushing or hub should drive wheels or gears.
Which shaft collar type suits a linear shaft?
A clamp collar, either one-piece or two-piece, suits a linear shaft. Set screws mark the shaft surface, and the burr they raise damages bushings and seals. A clamp spreads load over the whole bore, so there is no burr and the shaft survives repeated adjustment. On a precision shaft, a set screw should never sit directly on the running surface.
What is the difference between a set-screw collar and a clamp collar?
A set-screw collar holds by digging a screw tip into the shaft at one point, which raises a burr and leaves a dimple that marks the position. A clamp collar works by friction between its bore and the shaft, spreading the load over the whole bore. Holding power of a clamp collar is generally higher than a set-screw collar of the same size.
Can a shaft collar be the only stop against a heavy load?
No. Collars work well as stops for light loads, such as limiting the travel of a sliding carriage on a rod or setting the position of a bearing. A collar can slip under impact, so it should not arrest a moving mass. If a failure could cause a hazard, use a proper shoulder, a retaining ring in a groove or another positive stop.
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