Tension Sprockets

What is a tension sprocket?

A tension sprocket, also called an idler sprocket or tensioner sprocket, is a free-running sprocket that keeps a roller chain at the correct tension. Unlike a drive sprocket, it is not fixed to a driven shaft. Instead, it has a built-in ball bearing that lets it spin freely on a mounting bolt, and it is fitted to a tension arm that presses it against the chain. This takes up slack, maintains correct chain wrap around the sprockets, and keeps the drive running smoothly as the chain wears.

The tension sprockets in this range are designed to fit tension arms, such as SE15, SE18, and SE27 sizes. Each sprocket is matched to a specific chain pitch and is supplied with a mounting bolt and nuts, so it can be fitted straight onto the arm.

A typical tension sprocket has:

• Toothed rim - teeth that match the pitch and width of the roller chain
• Built-in bearing - a sealed ball bearing that lets the sprocket spin freely with the chain
• Mounting bolt and nuts - used to fix the sprocket to the tension arm
• Spacers or hub - help position the sprocket in line with the chain

Tension sprockets are usually described by:

• Chain size - the chain the sprocket suits, such as 06B (3/8 inch), 08B (1/2 inch), or 10B (5/8 inch)
• Number of teeth - such as 15 teeth
• Number of strands - simplex for single-strand chains, or duplex for double-strand chains
• Tension arm size - the tension arm the sprocket is designed to fit, such as SE15, SE18, or SE27
• Thread size - the size of the mounting bolt

For example, an 08B × 15T 1/2 inch sprocket for an SE27 tension arm suits 1/2 inch pitch 08B roller chain, has 15 teeth, and is designed to fit an SE27 tension arm.

Key features:

• Maintains chain wrap - keeps the chain engaged properly on the drive and driven sprockets
• Takes up chain stretch - compensates for slack as the chain wears
• Free running - a sealed bearing lets the sprocket turn smoothly with the chain
• Supplied with fixings - comes with a bolt and nuts for quick fitting to the tension arm
• Matched to tension arms - designed to suit standard tension arm sizes
• Reduces chain whip and noise - controls slack chain for smoother, quieter running
• Range of chain sizes - to suit common 3/8, 1/2, and 5/8 inch roller chains

In simple terms, a tension sprocket is a free-spinning sprocket that fits onto a tension arm to keep a chain tight, quiet, and running smoothly as it wears.

Why are tension sprockets essential?

Tension sprockets are essential because roller chains stretch as they wear, and a slack chain causes problems. A loose chain can whip, rattle, jump teeth, and wear the chain and sprockets quickly. In severe cases, it can come off the sprockets altogether. On drives with fixed shaft centres, there may be no other way to remove that slack. A tension sprocket on a spring-loaded or rubber-element tension arm keeps the chain at the right tension automatically, throughout its working life.

Their main benefits are:

• Longer chain and sprocket life - correct tension reduces wear on chains and sprockets
• Automatic adjustment - when fitted to a tension arm, takes up chain stretch without manual adjustment
• Smoother running - controls chain movement, reducing vibration and jerky operation
• Quieter drives - reduces chain slap and rattling
• Prevents tooth jumping - keeps the chain properly engaged with the sprockets
• No need to move machines - tension is maintained without moving motors or shafts
• Quick fitting - supplied with fixings to match the tension arm
• Reduced downtime - fewer chain problems and less maintenance

Tension sprockets are used across a wide range of industries and applications, including:

• Conveyors - roller chain drives on belt, roller, and slat conveyors
• Agricultural machinery - drives on balers, harvesters, drills, spreaders, and implements
• Packaging and food machinery - chain drives on production and packing lines
• Industrial machinery - mixers, feeders, and general chain drives
• Material handling - transfer and handling equipment
• Printing and textile machinery - chain drives and timing systems

The main types of tension sprockets

Tension sprockets are usually grouped by chain size, number of strands, and the tension arm they fit.

By chain size:

• 06B (3/8 inch) sprockets - for light-duty roller chain drives
• 08B (1/2 inch) sprockets - one of the most common sizes for general industrial and agricultural drives
• 10B (5/8 inch) sprockets - for heavier drives and higher loads
• Larger chain sizes - such as 12B and 16B for heavy-duty drives

By number of strands:

• Simplex tension sprockets - for single-strand roller chains
• Duplex tension sprockets - for double-strand roller chains on heavier drives

By tension arm size:

• Sprockets for smaller tension arms - such as SE15 and SE18 sizes, used on light and medium-duty drives
• Sprockets for larger tension arms - such as SE27 sizes, used on medium and heavier drives with larger chains

By bearing arrangement:

• Single bearing sprockets - a sealed ball bearing for general-duty use
• Double bearing sprockets - two bearings side by side for greater stability and load capacity

Related products:

• Tension arms - spring-loaded or rubber-element arms that hold the tension sprocket against the chain and adjust automatically as the chain stretches
• Tension rollers - plain rollers used to tension chains or belts
• Chain guides - guide and support chains along their path

How to choose the right tension sprocket?

Choosing the right tension sprocket means matching it to the chain and the tension arm. Work through these points in order:

• Chain size - choose a sprocket that matches the chain pitch exactly, such as 06B, 08B, or 10B
• Chain standard - check whether the chain is British Standard or ANSI, as they are not interchangeable
• Number of strands - choose simplex or duplex to match the chain
• Tension arm size - choose a sprocket designed for your tension arm, such as SE15, SE18, or SE27
• Thread size - check the mounting bolt suits the hole or slot in the tension arm
• Number of teeth - choose a sprocket size that fits the space and gives smooth chain movement
• Load and speed - choose a larger chain size, larger tension arm, or double bearing sprocket for heavier drives
• Environment - sealed bearings help protect against dust and dirt
• Quality and brand - choose sprockets from reputable suppliers for accurate teeth and reliable bearings

How to fit a tension sprocket

Fitting a tension sprocket correctly helps the chain run smoothly:

• Isolate the drive - switch off and isolate the machine before starting work
• Fit the sprocket to the arm - bolt the sprocket to the tension arm using the supplied bolt and nuts
• Choose the position - mount the tension arm so the sprocket runs on the slack side of the chain, not the tight side that carries the load
• Check the wrap - position the sprocket so the chain wraps around at least three teeth
• Align it - make sure the sprocket is in line with the drive and driven sprockets
• Set the preload - set the tension arm so it presses the sprocket against the chain with enough force to remove slack, following the tension arm manufacturer’s guidance
• Tighten the fixings - secure the sprocket and tension arm bolts firmly
• Check the drive - turn the drive by hand to check the chain runs smoothly without binding

FAQ - All you need to know about tension sprockets

What is a tension sprocket used for?

A tension sprocket keeps a roller chain at the correct tension and maintains chain wrap around the sprockets. It spins freely on a bearing and is usually fitted to a tension arm.

What do the sizes on a tension sprocket mean?

They usually show the chain size and the number of teeth. For example, 08B × 15T means the sprocket suits 08B, or 1/2 inch pitch, roller chain and has 15 teeth.

What are SE15, SE18, and SE27?

These are tension arm sizes. Tension sprockets are made to fit specific arm sizes, so check that the sprocket matches the tension arm you are using.

Does the tension sprocket come with fixings?

Yes. These tension sprockets are supplied with a mounting bolt and nuts for fitting to the tension arm.

Where should a tension sprocket be fitted?

It should be fitted on the slack side of the chain, which is the side not carrying the load. Make sure the chain wraps around at least three teeth.

What is the difference between a tension sprocket and a drive sprocket?

A drive sprocket is fixed to a shaft and transmits power. A tension sprocket spins freely on a bearing and only guides and tensions the chain.

How tight should the chain be?

The chain should have a small amount of slack, as recommended by the chain manufacturer. A chain that is too tight increases wear, while a chain that is too loose can whip and jump teeth.

Do tension sprockets need lubrication?

The sealed bearing does not usually need lubrication, but the chain running over the sprocket should be kept lubricated to reduce wear.

Why is my tension sprocket noisy?

Common causes include a worn bearing, misalignment, the wrong chain size, worn teeth, or incorrect tension. Check the sprocket and replace it if the bearing is rough or the teeth are worn.

When should I replace a tension sprocket?

Replace it if the bearing is rough, noisy, or loose, if the teeth are hooked or worn, or if the sprocket no longer runs smoothly. It is good practice to check the tension sprocket whenever the chain is replaced.