Types of Shaft Collars: A Complete Guide
A shaft collar is a ring-shaped component, usually metal, that clamps or screws onto a shaft to locate, space or stop another component. It looks like one of the simplest parts in any machine, and in a sense it is, but the type specified has a direct, measurable effect on how much axial load it can hold before it slips.
That difference is not small. Clamp-style shaft collars distribute their clamping force evenly around the full circumference of the shaft, which gives them roughly double the holding power of a set screw collar of the same size, according to manufacturer Ruland's own comparative testing. Choosing between the two, or between any of the half-dozen other styles now on the market, is less about personal preference than about matching the collar's mounting mechanism to the loads, shaft material and adjustment frequency the application actually needs.
Discover the Ruland range of shaft collars here
What Is a Shaft Collar?
A shaft collar, sometimes called a locking collar or shaft clamp, is a ring-shaped component that fits around a shaft and is fixed in place using either clamping force or a set screw, depending on the design. Once mounted, it locates or restrains whatever sits next to it on the shaft, whether that's a bearing, a sprocket, a sensor bracket or the shaft's own end travel.
Shaft collars turn up in almost every type of rotating machinery, from small servomotors to heavy conveyor drives. They are generally easy to install, adjust and remove, with minimal ongoing maintenance, which is part of why such a simple component ends up specified so often.
What Are Shaft Collars Used For?
The core job of a shaft collar is positioning. It holds a bearing, pulley, sprocket, or sensor at a fixed point on the shaft, keeping power-transmission components correctly aligned in motor and gearbox assemblies. That same holding power makes shaft collars useful as spacers, keeping two or more components at a set distance apart along the shaft.
They also serve as mechanical stops, limiting the travel of a reciprocating shaft in actuators and cylinders, which is common in automotive and heavy machinery applications. Because the underlying job, restraining or locating something on a shaft, is so universal, shaft collars appear across automotive, medical, packaging, food and beverage, and material handling equipment.
Types of Shaft Collars
Shaft collars fall into two broad mounting families: set screw and clamp-style. Within clamp-style, several further variants exist to suit different holding power, adjustment frequency and space requirements.
Set Screw Shaft Collars
Set screw shaft collars were the first type mass-produced, originally used on line shafting in early manufacturing mills. The earliest versions used protruding square-head screws that could catch a worker's clothing while the shaft was rotating, pulling them toward the machine. That risk was designed out between 1910 and 1911, when Howard T. Hallowell patented a shaft collar using a recessed hex socket set screw, a design that quickly became the industry standard and is still in use today.
A set screw collar's holding power comes entirely from the screw impinging into the shaft, so it depends on the shaft being made from a softer material than the screw itself. Where that's true, set screw collars offer strong torque capacity and handle shock loads well, which is why they remain common on unhardened shafts. The trade-off is that the impingement raises a small burr on the shaft surface, which makes fine adjustment difficult and permanently marks the shaft, and they cannot be used on hardened shafts at all since the screw has nothing softer to bite into.
Clamp-Style Shaft Collars
Clamp-style collars were developed to solve the marring problem, mounting using compression rather than a screw driven into the shaft. Because the clamping force is spread evenly around the shaft's circumference rather than concentrated at one point, clamp-style collars deliver roughly double the holding power of a set screw collar of the same size, and they can be removed, repositioned and reinstalled without damaging the shaft.
One-piece clamp collars
One-piece clamp collars wrap fully around the shaft and use a single screw. Below roughly 1-5/8 inches (38mm) bore, they're typically machined with a back-cut opposite the clamp gap, which reduces the material the screw has to flex, letting more of the screw's seating torque go directly into clamping force rather than bending the collar itself.
Two-piece clamp collars
Two-piece clamp collars split into two halves, so the collar can be fitted or removed without sliding it off the end of the shaft or disturbing other components already mounted. The second screw improves holding power over a one-piece design, though only by around 5%, so the choice between one-piece and two-piece usually comes down to whether the assembly needs to come apart without disturbing anything else, not raw holding power.
Quick clamping collars
Quick clamping collars, using a cam lever or a ratcheting clamping lever, allow tool-free adjustment in seconds rather than minutes, which suits printing, packaging and other applications with frequent setup changes. The trade-off is lower holding power than a standard clamp collar and unsuitability for rotating applications, so they're a light-duty, positioning-only choice.
Heavy Duty, Thin Line and Double Wide Shaft Collars
Where an application needs more or less holding power than a standard collar provides, width and diameter become the levers. Heavy duty collars use a larger outer diameter and wider body to accommodate bigger, stronger screws, making them the standard choice for large shafts, typically above 3 inches (75mm), where a standard collar's screw size becomes the limiting factor.
Double-wide collars take the opposite approach to a heavy-duty collar's diameter increase, adding width and a second pair of screws instead, which can raise holding power by as much as 25% over a standard single-width collar of the same diameter. At the other end of the spectrum, thin line collars trade holding power for a reduced width, diameter and screw size, which suits space or weight-constrained applications such as encoders, where the load requirement is genuinely low.
Threaded Shaft Collars and Bearing Locknuts
Threaded collars use a matching thread on the shaft rather than friction alone, creating a positive mechanical stop that's far harder to shift under shock loading than a round-bore collar relying on clamping force. That makes them well suited to high axial-load applications and to fine preload adjustment, since the collar can be threaded to an exact position and then locked with its clamp screw.
Bearing locknuts are specialised threaded collars, manufactured to AFBMA standards in industry-standard N00 to N14 sizes, designed to mate with precision spindle bearings on CNC mills and lathes. They hold a tighter TIR than a standard shaft collar, which is what lets them apply even pressure across the entire bearing face while precisely controlling preload, with spanner wrench slots machined into the outer diameter for fine adjustment.
Keyed, Hex and D-Bore Shaft Collars
Keyed shaft collars incorporate a keyway to prevent slippage in positive-drive applications, which matters where torque transmission, not just axial positioning, is the collar's job. Hex and D-bore collars serve a similar purpose on non-round shafting: a hex bore collar gives higher torque capacity on hex shafting than a round-bore set screw collar could achieve, while a D-bore clamp collar can replace a traditional set screw collar on D-shaft profiles, offering more even surface contact and higher holding power without marring the flat.
Mountable Shaft Collars
Mountable collars add flats and through-holes, or face holes, to the standard collar body, letting sensors, brackets, sprockets or plates be bolted directly to the collar rather than mounted separately on the shaft. This is a convenience and space-saving feature rather than a holding power upgrade, and it has no significant impact on the collar's core clamping performance.
How to Choose the Right Shaft Collar
Once the mounting mechanism is decided, four further factors determine whether a specific shaft collar will perform: holding power, face-to-bore perpendicularity, material, and the operating environment.
Ranked from lowest to highest holding power under comparable conditions, the order runs roughly: quick clamping, set screw, thin line, standard clamp, double wide, heavy duty, then threaded or bearing locknut collars, according to Ruland's own comparative guidance. A set screw collar's holding power is governed almost entirely by the relative hardness of the screw and the shaft. A clamp-style collar's holding power is governed more by bore size, concentricity and the quality of the fastening hardware, since forged screws hold their torque rating more consistently than broached ones and are less prone to reaming out under repeated use.
Face-to-bore perpendicularity matters wherever the collar sits against a load-bearing face, such as a precision bearing or an axial stop in a pneumatic cylinder. A collar with poor perpendicularity applies uneven pressure across the interface, which shortens the life of whatever it's seated against and can let the collar "walk" along the shaft under repeated axial force. A TIR of 0.002 inches (0.05mm) or tighter is the benchmark for these high-leverage applications.
Surface treatment affects holding power as much as the base material does. Black oxide is an anti-stick-slip finish that helps a screw hold its intended torque rating, whereas zinc plating, while more corrosion-resistant, reduces the collar's friction coefficient and therefore its holding power. It's also worth checking the screws, not just the collar: a corrosion-resistant collar paired with an untreated screw will still fail prematurely in a harsh environment, since the screw is usually the first component to corrode.
Where to Buy Genuine Shaft Collars
Precision motion components are a documented target for counterfeiting. SKF's own brand protection efforts have identified customs seizures worth millions of dollars in counterfeit bearings and related components, and the wider counterfeit parts market causes financial losses for legitimate manufacturers and buyers alike through reduced service life, unexpected failures and voided warranties, since counterfeit parts are rarely built to the original manufacturer's tolerances or material specification.
At ACORN, we supply the genuine Ruland range of shaft collars, sourced directly to guarantee the material, torque rating and perpendicularity specification match what's on the datasheet. Contact our specialist couplings division for advice on specifying the right type, material and size for your application.
Frequently Asked Questions
What are the different types of shaft collars?
The main types are set screw collars, one-piece and two-piece clamp-style collars, quick clamping collars with a cam or clamping lever, heavy-duty, thin line and double wide collars, threaded collars and bearing locknuts, and keyed, hex and D-bore collars for non-standard or positive-drive shafting. Mountable collars add flats or face holes for attaching sensors or brackets directly.
What's the difference between a set screw collar and a clamp collar?
A set screw collar is held in place by a screw that bites directly into the shaft, which permanently marks the shaft and requires the shaft to be softer than the screw. A clamp-style collar uses compressive force distributed around the full circumference of the shaft instead, which doesn't damage the shaft, works on shafts of any hardness, and typically provides around double the holding power of a set screw collar of the same size.
What is a quick clamping shaft collar used for?
Quick clamping collars use a cam lever or a ratcheting clamping lever to allow tool-free adjustment, which suits applications with frequent setup changes, such as printing and packaging machinery. They have less holding power than a standard clamp collar and are not recommended for rotating applications, making them a positioning tool rather than a high-load holding solution.
What is a bearing locknut, and how is it different from a standard shaft collar?
A bearing locknut is a threaded shaft collar manufactured to AFBMA standards in industry-standard N00 to N14 sizes, specifically designed to mate with precision spindle bearings on CNC mills and lathes. It holds a tighter face-to-bore perpendicularity than a standard collar, which lets it apply even pressure across the bearing face and precisely control preload, with spanner wrench slots for fine adjustment.