E30 Zone

hello people again i have just bought some sport suspension for my e30 and the company i have bought it from have emailed me this:

These are in stock but there is a choice of two shock absorbers for the front. I need you to tell me the diameter of your front strut assembly. The choices are 45mm or 51mm.

now my bmw is a 325i convertible it is a 1986 now i dont know what to do or how does anyone know thanks

It's 51mm

thanks mate