Instead of using screws for the H516 (which then holds C516 microphone) I always go for this rubber plates. Ive been using several of them on different instruments, although the main use is for accordion. The vibrations from the instrument transfered to the microphone are then heavily reduced. The glue is quite good, and I only had once the problem where the rubber plate deatached from the H516, but never from the instrument.
These rubber replacement pads that are used in conjunction with the h516 plate are excellent as they help reduce extraneous noise and vibrations from knocking the surrounding area around the base of the plate. I would highly recommend these to anyone using the c516 and b29 battery pack and microphone system. As my collection of accordions has grown over the past 5 years I've bought extra plates and pads do that I can simply move the akg c516 microphones I own from one instrument to another as and when required. I highly recommend these pads if you're going to add the plates in this fashion. Definitely recommend getting them and I always have a few in reserve.