Easy to install Frankford Arsenal powder drop micrometer lock stops the micrometer from moving on long load sessions to combat powder weight drift. The locks work with the X-10 press powder drops and the Frankford Arsenal bench mount powder drops both.
 
The lock installs easily with two screws, loosen the screws enough to let your micrometer move, set your desired powder charge, tighten the screws to lock the micrometer.
 
They are designed to fit multiple variances in micrometer cap sizes so it is normal for some to show a gap between the halves when properly tightened than others.