Is there actually an difference between the 2?

You see some listed as fitting any and some lisetd to fit only one.

Most manufactures do differ the bore size between the 40mm and the 45mm. however they are interchangeable due to using the same bolt holes.

I would advise buying the size you need as using the wrong one will inhibit performance.

Also be very careful:
if you are going to buy one as I have had a few that have been very poor quality castings and i have had to spend hours cleaning them up to an almost polished look which looked daft when nothing else was shiny!!

cheers,

Dubstar_04

I thought they must be different bore sizes.