It's plastic...I took it to the store- it's 36mm in case anyone else needs to know.
<img src='http://www.bmw-forums.com/forum/uploads/photo-1876.jpg' border='0' alt='user posted image' />
'97 328ic 5-Speed Sport- 30K Miles! It's a babe...The mods have begun!: Clear corners/tails/markers- Hella Heads- Breyton Strut Bar/Rogue SS Cat Back/Conforti Intake/Brembo X-drilled Rotors- Axxis Ceramics- Red Calipers/Michelin Pilot Sports/Alpine-MBQuart Stereo upgrade/Euro Evo II M-Tec Steering wheel...more soon!