Shaft Collars

What is a shaft collar?

A shaft collar is a simple ring that fits around a shaft and locks onto it, creating a fixed shoulder or stop at any point along its length. Shaft collars are used to position and retain components such as bearings, pulleys, sprockets, gears, and bushes, to stop shafts moving sideways in their bearings, to act as mechanical stops that limit travel, and to space parts apart along a shaft. Although they are one of the simplest components in power transmission, they play an important role in keeping machinery aligned, secure, and working correctly.

The most common type is the set screw shaft collar, a solid steel ring with a threaded hole through one side. A grub screw, also called a set screw, is tightened through the hole so that its tip presses against the shaft, locking the collar in place. Other designs clamp around the shaft instead, spreading the holding force evenly without marking the shaft.

Shaft collars are usually described by three dimensions:

• Bore - the inside diameter, which must match the shaft diameter
• Outside diameter - the overall diameter of the collar, which sets the size of the shoulder it creates
• Width - the thickness of the collar along the shaft

For example, a 5 × 10 × 6 mm shaft collar has a 5 mm bore to fit a 5 mm shaft, a 10 mm outside diameter, and a 6 mm width. Imperial collars are described in the same way, such as 1/4 × 1/2 × 9/32 inch.

A typical set screw shaft collar has:

• Collar body - a solid ring, often made from En8 steel with a zinc plated finish for strength and corrosion resistance
• Precision bore - machined to slide easily onto the shaft with a close fit
• Threaded hole - drilled and tapped through the side of the collar
• Grub screw - usually a hex socket set screw with a cup point that bites into the shaft to hold the collar in place
• Chamfered edges - help the collar slide on easily and remove sharp corners

Key features:

• Positions components - holds bearings, pulleys, gears, and other parts at an exact position on the shaft
• Prevents axial movement - stops shafts and components sliding sideways
• Acts as a stop - limits the travel of moving parts
• Adjustable - can be fixed anywhere along a plain shaft and repositioned as needed
• No shaft machining needed - removes the need for shoulders, grooves, or circlips on the shaft
• Quick to fit - fitted with a simple hex key or screwdriver
• Metric and imperial sizes - available to suit a wide range of shafts
• Low cost - an economical solution for positioning and retaining parts

In simple terms, a shaft collar is a ring that locks onto a shaft to hold parts in place, stop sideways movement, or act as an adjustable stop.

Why are shaft collars essential?

Shaft collars are essential because shafts and the parts mounted on them need to stay in the right place. Without a way to hold them, shafts can slide sideways in their bearings, pulleys and sprockets can move out of line, and moving parts can travel too far. This can cause belts and chains to run off, bearings to wear unevenly, gears to mesh poorly, and machinery to jam or fail. Shaft collars provide a simple, adjustable way to prevent these problems without the cost of machining shoulders or grooves into the shaft.

Their main benefits are:

• Accurate positioning - keeps components exactly where they need to be on the shaft
• Prevents shaft float - stops shafts moving sideways in bearings and bushes
• Protects alignment - keeps pulleys, sprockets, and gears in line, reducing belt, chain, and gear wear
• Reduces machining - avoids the need for shaft shoulders, grooves, or threaded ends
• Easy adjustment - collars can be moved and refixed during set-up and maintenance
• Simple maintenance - parts can be removed and refitted quickly
• Versatile - used as stops, spacers, retainers, and mounting points
• Cost-effective - an inexpensive way to solve many positioning problems

Shaft collars are used across a wide range of industries and applications, including:

• Bearing assemblies - retaining bearings and bushes on shafts and stopping shafts sliding through bearings
• Belt and chain drives - positioning pulleys and sprockets and keeping them aligned
• Gearboxes and gear drives - locating gears on shafts
• Conveyors - retaining rollers, shafts, and sprockets
• Packaging and food machinery - positioning shafts, guides, and moving parts
• Automation and robotics - acting as stops and locating parts on linear and rotary shafts
• Agricultural machinery - retaining shafts, linkages, and pivots
• Fitness and leisure equipment - positioning and retaining moving parts and adjustable mechanisms
• Model engineering, 3D printers, and hobby CNC - locating shafts and parts in small machines
• Workshop tools - acting as depth stops and positioning guides

The main types of shaft collars

Shaft collars are usually grouped by how they fix to the shaft, their material, and their finish.

By fixing method:

• Set screw shaft collars - solid collars held in place by a grub screw that presses against the shaft. They are simple, compact, and economical, and the most common type for general use. Many follow the DIN 705 standard for adjusting rings
• Set screw collars with two screws - use two grub screws, often at 90 degrees, for greater holding power and resistance to loosening
• One-piece clamp collars - have a split on one side and a clamping screw that tightens the collar around the shaft. They grip evenly all the way around, giving better holding power without marking the shaft
• Two-piece clamp collars - made in two halves held together by two screws. They can be fitted and removed without sliding them along the shaft, which is useful when other components are already in place
• Quick-release collars - use a lever or hinged design for fast adjustment without tools, ideal for parts that need to be repositioned often
• Threaded collars - have a threaded bore that screws onto threaded shafts, ideal for precise positioning and high axial loads
• Flanged and mounting collars - have tapped holes or a flange, allowing other parts to be bolted directly to the collar

By material:

• En8 steel collars - a medium carbon steel with good strength and machinability, widely used for general engineering. Usually zinc plated or black oxide finished for corrosion protection
• Mild steel collars - an economical choice for light-duty applications
• Stainless steel collars - resist rust and corrosion, ideal for food processing, marine, medical, and washdown environments
• Aluminium collars - lightweight and corrosion resistant, used where low weight or low inertia is important
• Plastic collars - made from engineering plastics such as nylon or acetal, lightweight, corrosion resistant, and non-marking, used for light loads

By finish:

• Zinc plated - a bright, silver finish that gives good corrosion protection for indoor and general use
• Black oxide - a dark finish with light corrosion protection, often used in machinery
• Self-colour - a plain finish, usually lightly oiled
• Polished stainless - a clean, corrosion-resistant finish for hygienic environments

By size system:

• Metric shaft collars - with bores in millimetres, such as 5, 6, 8, 10, 12, 16, 20, and 25 mm
• Imperial shaft collars - with bores in inches, such as 1/4, 5/16, 3/8, 1/2, 5/8, and 3/4 inch

How to choose the right shaft collar?

Choosing the right shaft collar means matching it to the shaft, the load, and the job it needs to do. Work through these points in order:

• Shaft diameter - choose a collar with a bore that matches the shaft diameter exactly. Measure the shaft with calipers or a micrometer, as even a small difference affects the fit
• Metric or imperial - check whether the shaft is metric or imperial, as sizes such as 6 mm and 1/4 inch are close but not interchangeable
• Outside diameter - choose an outside diameter large enough to create the shoulder or stop you need, but small enough to fit the available space
• Width - wider collars give more contact area and stability, while narrower collars save space
• Holding power - choose a set screw collar for general use, a clamp collar for higher holding power, or a collar with two screws where vibration is a concern
• Shaft protection - choose a clamp collar if you do not want to mark the shaft, or if the collar will be moved often
• Shaft hardness - clamp collars usually work better on hardened shafts, as set screws cannot bite into hard surfaces as effectively
• Fitting access - choose a two-piece clamp collar if the collar must be fitted or removed without taking other parts off the shaft
• Axial load - check that the collar can resist the sideways forces in the application. For high axial loads, consider wider collars, clamp collars, threaded collars, or a machined shoulder
• Speed - for high-speed shafts, consider balanced or clamp-style collars, as set screws can create imbalance
• Material and finish - choose zinc plated En8 steel for general use, stainless steel for wet or corrosive environments, aluminium for low weight, or plastic for light, non-marking applications
• Safety - on exposed rotating shafts, consider guarding, as projecting set screws can catch clothing and hair
• Quality and brand - choose collars from reputable suppliers for accurate bores, square faces, and reliable screws

How to fit a shaft collar

Fitting a set screw shaft collar is quick and simple:

• Clean the shaft - remove dirt, burrs, and excess oil where the collar will sit
• Slide the collar on - push it along the shaft to the required position, with the chamfered side facing the part it locates if possible
• Position it - set the collar against the bearing, pulley, or part, allowing any recommended clearance
• Tighten the grub screw - tighten it firmly with the correct hex key or screwdriver. Avoid overtightening, which can damage the screw or thread
• Add security if needed - for vibrating machinery, apply a thread locker to the grub screw, or use a second screw
• Improve grip on smooth shafts - where extra holding power is needed, a small flat machined on the shaft under the grub screw gives the screw a better seat
• Check the fit - turn the shaft by hand to make sure the collar is secure and does not rub on housings or other parts

FAQ - All you need to know about shaft collars

What is a shaft collar used for?

A shaft collar is used to position and retain parts on a shaft, stop shafts moving sideways in their bearings, act as a mechanical stop, or space parts apart along a shaft.

What do the sizes on a shaft collar mean?

Shaft collar sizes are usually given as bore × outside diameter × width. For example, 5 × 10 × 6 mm has a 5 mm bore, a 10 mm outside diameter, and a 6 mm width.

What is En8 steel?

En8 is a medium carbon steel that offers good strength, toughness, and machinability. It is widely used for engineering components such as shaft collars, shafts, and studs.

Why are shaft collars zinc plated?

Zinc plating protects the steel from rust and corrosion and gives a clean, bright finish. It is suitable for indoor and general use, while stainless steel collars are better for wet or corrosive environments.

What is the difference between a set screw collar and a clamp collar?

A set screw collar is held by a grub screw that presses into the shaft. A clamp collar is split and tightened around the shaft with a clamping screw, giving more even grip, higher holding power, and no marks on the shaft.

Will a set screw collar damage my shaft?

The tip of the grub screw can leave a small mark on the shaft. This is usually not a problem, but if the collar needs to be moved often, or the shaft must stay undamaged, a clamp collar is a better choice.

Can I use a shaft collar on a hardened shaft?

Yes, but set screws may not grip hardened shafts as well. Clamp collars usually give better holding power on hardened shafts.

How do I stop a shaft collar from slipping?

Make sure the bore matches the shaft size, tighten the grub screw firmly, and consider a thread locker on the screw. For more grip, use a collar with two screws, a clamp collar, or machine a small flat on the shaft under the screw.

Can I use a metric collar on an imperial shaft?

It is not recommended. Metric and imperial sizes may look similar, but even a small difference in bore size can cause a loose fit and poor holding power. Always match the collar to the shaft size.

Can shaft collars carry heavy axial loads?

Shaft collars can resist moderate axial loads. For heavy axial loads, choose wider collars, clamp collars, or threaded collars, or consider a machined shoulder or other fixed location on the shaft.

Are shaft collars safe on rotating shafts?

Yes, but projecting set screws on fast-rotating shafts can catch clothing, hair, or tools. Use collars with recessed screws or clamp collars, and fit guards where shafts are exposed.

Can shaft collars be reused?

Yes. Shaft collars can usually be removed and refitted many times. Replace the grub screw if its tip or hex socket is worn or damaged.