43mm

I am planning to get Driven clipons. They come in sizes from 43mm to 55mm. What's the right size? Would 43mm work?

Hi guys! Anyone knows what is the size of aftermarket clip-on for a RC 390? I have seen 51 mm in many cases but also 43mm? Sorry if the question have allready been answered but I just want to make sure before ordering. Thanks for your help.