Here we have set of chrome tailpipe trims that fits many M cars, non M performance exhaust, I had them on my F80 M3 an they looked great, I measure them at 90mm or 3.5" at the outlet and 70mm inlet.

Someone has replaced one of the bolts for some reason but they work fine.

Burkhart Engineering individual tailpipe set for the F87 M2 & M2 Competition, F80 M3 and F82/F83 M4
90mm slant cut tips

Thanks for looking.