7/8"-27 female flange with base holes on 1 1/4" centers. This flange allows microphone stange to be secured to the flor of areas like drum risers where there is not enogh space for a weighted microphone stand base. The QR-2F can be mounted with the 7/8"-27 threaded boss above the floor or resssed in the floor. I can also be used with the QR-2 Quick Release Mic Stand Adapter to improve setup and teardown time.