How do you know the size of the sprocket?

Answer 1

The most commonly used characteristic is the tooth count.

A vernier caliper would be my choice for measuring the thickness of the sprocket (which has to work with the width of the chain) for which there are several options available depending on bike/drivetrain type.

the 3rd size it can be helpful to know is how the sprocket attaches to the hub. Again several options available. But knowing which kind of drivetrain it is should usually be enough to get you the right part.

Answer 2

Depends on what you mean by "size". What's most usually discussed is tooth count, and to find that out - well, you count the teeth. As simple as that.

You might also be asking about the size where the sprocket attaches to either the hub or the cranks (depending on if you're talking about a BMX or any other kind of bike). and in that case you'll either have to measure, or track down a specification on the bike.

Answer 3

There are two common standards for pedal threads, 9/16 and 1/2. But the only sure way of finding out what you've got (unless someone knows your exact make of crank) is to remove one and measure it. Pedals can be stuck on real bad, and remember that the left one unscrews clockwise.

Answer 4

Crank arm length is usually embossed on the inside of the crank arms, and the most common sizes are 170 and 175 mm. Chainring size is trickier. 4-hole rings are fairly easily measured, but 5-holes are awkward.

Answer 5

The width you can get with a vernier caliper, the length by counting the links. The pitch you get by measuring the distance from one roller to the next.