motorbike chain designation is a rather odd system.
It's a 3 digit number.
The first digit is the number of 1/8" in the pitch (i.e. distance between the pins along the chain), so a 4** chain is 1/2" pitch, a 5** is 5/8" and a 6** is 3/4" pitch.
The second and third digits are the number of 1/8" in the width (in effect the thickness of the sprockets) in a decimal format without the decimal point, so a *20 is 2.0 times 1/8" = 1/4", a *25 is 2.5 times 1/8" = 5/16", and a *30 is 3.0 times = 3/8".
Thus a 525 is 5/8" pitch and 5/16" width.
The overall width of the chain itself will depend on how thick the various sideplates and linkplates are, which can be different for normal and heavy duty etc.
http://www.tsubaki-rider.com/download/ROADbrochure.pdf
I didn't make the system up!
