How Do I Know What Size Sprocket I Need?

Chain size, type, number of teeth, and bore size are all you need to select the correct roller chain sprocket.

Idler Roller Chain SprocketsWhen you look at sprockets on a product page or catalog, you’ll see a string of numbers and letters. Let’s break one down. #50BB15x1/2” is one of the seventeen idler roller chain sprockets currently available for order on our website. The “#50” is an ANSI designation for the pitch of the chain this sprocket is meant to carry. The ANSI system takes in the chain pitch expressed as eighths-of-an-inch, grabs the numerator and multiplies it by 10 to get the chain designation. So, working backwards, a #50 chain has a 5/8” pitch, which is what this example sprocket is built to handle (If you need to measure your chain pitch before you can order the sprocket, check out the roller chain sizing guide here). ANSI chain designations over 80 map to a pitch greater than 1”.

Next up is the type of sprocket. The “BB” in this case is for “ball bearing”: it’s an idler sprocket, which means it’s more of a guide than a driver, and the ball bearing ensures clean, balanced movement. Taper-lock sprockets will have “BTL” in their designation, finish bore sprockets have “FB” and QD-bushed sprockets have “JA” (because someone always has to be different).

After the sprocket type is the number of teeth. QD-brushed and taper-lock sprockets have those three components in their name. But FB and BB sprockets have one more piece of information: bore size. MDS carries sprockets with bore sizes 1/2” – 2”.

To recap, then, if you order a #50BB15x1/2” sprocket from MDS, you’ll receive an idler sprocket with 15 teeth and a 1/2″ bore to be used with a chain that has a 5/8” pitch.

Contact MDS if you need to talk over your roller chain or sprocket needs, and we’ll make sure you have the right sprocket in the right size.

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