Simplex Sprockets

What is a simplex sprocket?

A simplex sprocket is a sprocket with a single row of teeth, designed to run with simplex roller chain. Simplex chain is the most widely used type of roller chain, and simplex sprockets are found on a huge range of machines, from small mechanisms and garden equipment to agricultural machinery, conveyors, and industrial drives. The sprocket’s teeth mesh with the chain rollers, so as the drive sprocket turns, it pulls the chain along and drives the sprocket on the other shaft.

The simplex sprockets in this range have a hub and a pilot bore. The pilot bore is a small starter hole that can be machined out to fit the exact shaft size, with a keyway and set screw added as needed. This makes them very versatile for new drives, repairs, and custom applications.

A typical simplex sprocket has:

• Single row of teeth - matched to the pitch, roller size, and inner width of simplex roller chain
• Hub - an extended boss that supports the sprocket on the shaft and provides room for a keyway and set screw
• Pilot bore - a small starter bore that can be machined to the required shaft size
• Steel body - strong and durable, often with hardened teeth for longer wear life

Simplex sprockets are usually described by:

• Chain size - such as 04B for 6 mm pitch, 05B for 8 mm pitch, 06B for 3/8 inch pitch, or 08B for 1/2 inch pitch British Standard simplex chain
• Number of teeth - such as 9, 10, 13, or 18 teeth, which sets the sprocket size and drive ratio
• Bore type - such as pilot bore, ready to be machined to size
• Pitch circle diameter - the effective working diameter of the sprocket

For example, a 10 tooth 05B simplex pilot bore sprocket has 10 teeth, suits 8 mm pitch British Standard simplex chain, and has a pilot bore that can be machined to fit the shaft.

Key features:

• Simplex chain compatibility - a single row of teeth for standard roller chain drives
• Positive drive - meshing teeth give accurate, slip-free power transmission
• Pilot bore - can be machined to fit the shaft exactly, with a keyway and set screw added
• Hub design - gives a solid, stable mounting on the shaft
• Wide range of sizes - from small 6 mm and 8 mm pitch sprockets to large industrial sizes
• Steel construction - strong and durable for general engineering and agricultural drives

In simple terms, a simplex sprocket is a single-row sprocket that drives simplex roller chain to transmit power between shafts.

Why are simplex sprockets essential?

Simplex sprockets are essential because chain drives are one of the most reliable and cost-effective ways to transmit power. Sprockets and roller chain give positive drive with no slipping, so they keep timing accurate and transmit high torque, even at low speeds. They can work in dirty, dusty, and outdoor conditions, run over long centre distances, and drive several shafts at once. Simplex sprockets offer all these benefits in the simplest and most widely used form.

Their main benefits are:

• Positive drive - no slipping, keeping drives accurate and reliable
• High efficiency - transmits power with very little loss
• Speed and torque control - different tooth counts reduce or increase speed and torque
• Works in tough conditions - suits dust, dirt, and outdoor use
• Custom bores - pilot bores can be machined to suit any shaft size within the sprocket’s range
• Strong mounting - the hub gives a secure fit on the shaft with a key and set screw
• Cost-effective - economical to buy, fit, and replace
• Widely available - standard sizes make replacement sprockets easy to source

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

• General engineering - drives on industrial machinery
• Agricultural machinery - drives on drills, balers, harvesters, spreaders, and implements
• Conveyors - conveyor drives and transfer systems
• Packaging and food machinery - drive and timing systems on production lines
• Garden machinery - drives on mowers, cultivators, and other equipment
• Automation and small machinery - compact drives using small pitch chains
• Doors, gates, and lifting equipment - chain-driven openers and mechanisms
• Printing and textile machinery - drive and timing systems

The main types of simplex sprockets

Simplex sprockets are usually grouped by chain standard, chain size, tooth count, and bore type.

By chain standard:

• British Standard (BS) simplex sprockets - suit European-style simplex roller chains, such as 04B-1, 05B-1, 06B-1, 08B-1, 10B-1, 12B-1, and 16B-1
• ANSI simplex sprockets - suit American-style simplex roller chains, such as 25-1, 35-1, 40-1, 50-1, 60-1, and 80-1

British Standard and ANSI chains are not interchangeable, so the sprocket must match the chain standard.

By chain size:

• 04B (6 mm pitch) sprockets - for small, light-duty drives and compact mechanisms
• 05B (8 mm pitch) sprockets - for small and light-duty drives
• 06B (3/8 inch pitch) sprockets - for light and medium-duty drives
• 08B (1/2 inch pitch) sprockets - a popular size for general industrial and agricultural drives
• 10B (5/8 inch pitch) sprockets - for higher power drives
• 12B (3/4 inch pitch) and larger sprockets - for heavier drives

By number of teeth:

• Small sprockets - fewer teeth, used as drive sprockets on motors and gearboxes where space is limited
• Large sprockets - more teeth, used as driven sprockets to reduce speed and increase torque, and for smoother running

By bore type:

• Pilot bore sprockets - supplied with a small starter bore, ready to be machined to the exact shaft size, with a keyway and set screw added as needed
• Tapered bore sprockets - designed to accept a tapered locking bush for quick, keyless mounting

Related products:

• Simplex tapered bore sprockets - simplex sprockets designed for tapered locking bushes
• Simplex platewheels - hubless simplex sprockets that can be bored, welded, or bolted
• Simplex idler sprockets - free-running sprockets for guiding and tensioning chain
• Simplex chain and links - matching chain and connecting links for simplex drives

How to choose the right simplex sprocket?

Choosing the right simplex sprocket means matching it to the chain, the shaft, and the drive. Work through these points in order:

• Chain standard - check whether the drive uses British Standard or ANSI simplex chain
• Chain size - choose a sprocket that matches the chain pitch exactly, such as 05B or 08B
• Number of strands - make sure the sprocket is simplex, with a single row of teeth
• Number of teeth - choose tooth counts on the drive and driven sprockets that give the required ratio. As a guide, larger tooth counts give smoother running and less chain wear, especially at higher speeds
• Bore - check the pilot bore can be machined to your shaft size, leaving enough material in the hub for strength and a keyway
• Fixing method - plan how the sprocket will be fixed to the shaft, usually with a key and set screw
• Load and speed - check the chain size and sprocket suit the power and speed of the drive
• Space - check the pitch circle diameter, hub, and overall width fit the available space
• Quality and brand - choose sprockets from reputable suppliers for accurate teeth and reliable performance

How to fit a simplex sprocket

Fitting a simplex sprocket correctly helps the chain run smoothly:

• Machine the bore - bore the sprocket to the shaft size, keeping the bore concentric with the teeth
• Cut a keyway - add a keyway to suit the shaft key, and drill and tap a hole for a set screw if needed
• Isolate the drive - switch off and isolate the machine before fitting
• Fit to the shaft - slide the sprocket onto the shaft with the key in place
• Align the sprocket - position the sprocket so it lines up with the sprocket it drives, using a straight edge across the faces
• Secure the sprocket - tighten the set screw onto the key or shaft to stop the sprocket moving along the shaft
• Fit the chain - fit the simplex chain and set the tension, leaving a small amount of slack on the slack side
• Check the drive - turn the drive by hand to check the chain runs smoothly, then lubricate before running

FAQ - All you need to know about simplex sprockets

What is a simplex sprocket?

A simplex sprocket is a sprocket with a single row of teeth, designed to run with simplex roller chain to transmit power between shafts.

What does pilot bore mean?

A pilot bore is a small starter hole in the centre of the sprocket. It is designed to be machined out to the exact shaft size, usually with a keyway and set screw added.

What do 04B and 05B mean?

04B and 05B are British Standard chain sizes. 04B has a 6 mm pitch and 05B has an 8 mm pitch. They are used on small, light-duty drives and compact mechanisms.

What does 08B mean on a simplex sprocket?

08B is the British Standard chain size for 1/2 inch pitch chain. A simplex sprocket marked 08B suits 08B-1 simplex roller chain.

Can I use a simplex sprocket with duplex or triplex chain?

No. Simplex sprockets have a single row of teeth and are designed to run with simplex chain only.

What is the difference between BS and ANSI sprockets?

BS sprockets suit British Standard chain, and ANSI sprockets suit American Standard chain. They have different tooth dimensions and are not interchangeable.

What is the difference between pilot bore and tapered bore sprockets?

Pilot bore sprockets are machined to fit the shaft and fixed with a key and set screw. Tapered bore sprockets accept a tapered locking bush, giving quick, keyless mounting and allowing one sprocket to fit different shaft sizes.

How do I work out the drive ratio?

Divide the number of teeth on the driven sprocket by the number of teeth on the drive sprocket. For example, a 10 tooth drive sprocket and a 30 tooth driven sprocket give a 3:1 ratio, reducing speed to a third and increasing torque.

Why should I avoid very small sprockets?

Sprockets with very few teeth cause the chain to bend more sharply, which increases wear, vibration, and noise. Where space allows, larger sprockets give smoother running and longer chain life.

Do simplex sprockets need lubrication?

The chain running on the sprocket should be lubricated regularly to reduce wear. The sprocket itself does not need separate lubrication.

When should I replace a simplex sprocket?

Replace it if the teeth are hooked, pointed, or worn, as worn sprockets quickly wear new chain. It is good practice to check sprockets whenever the chain is replaced.