These useful clamps can be put to multiple uses round the studio they fit to most standard light stands and can be used to hold boom arms in place clamp has 4 different diameter holes for locking different sized boom arms and stands the clamp can be fully rotated to any angle you require hole diameters are 31 24 20 17mm please note that these the tightening method of the lock nut will compensate for a few mm with stands bigger in diameter to the hole sizes stated phot r products come