In message .com,
writes
Thanks for your reply Grunff. For interest though my maths for the
above is as follows.

Circumference = PI * diameter

so for the 160 diameter trend, we get

3.142 * 160mm = 502.72 mm for the circumference.

Now there are 48 teeth around the circumference so

48/502.72 = 0.09548 teeth per centimetre.

This is a case of taking a step back and looking at your answer

You're saying the teeth are 10cm apart

you've dropped from mm to cm

--
geoff