You didnt mention the year or application. I looked up a 2000 GXP L67, and found a stud PN 24504462 for the throttle body to supercharger. Go to gmpartsdirect.com to verify that your application uses the same part number.
Anyhow, for a PN 24504462, this is threaded M6x1.0 on both sides. 9.5mm...