In this video, Joel Grimes suggests ways to keep your strobe from rotating while affixed to the end of a boom pole. While the first technique (grinding the stud) he suggests will work, it's not the ideal method. In fact, of the three methods he suggests, none of them are as good as the simplest answer – get a baby drop-down pin.
The drop-down mounts to the end of your boom and allows you to affix your strobe and modifier so that they're hanging vertically, avoiding the stresses that cause your strobe to twist if mounted directly to the boom pole. Plus, since the drop-down pin swings freely, it stays in place (hanging straight down) as you change the angle of the boom. A drop-down pin has been part of my kit for many years now; it has a permanent home in my monolight bag and is utilized any time I pull out the boom. [Sean]