Fits around sound hole in front bass drum head, to reinforce it, keep it from splitting.  

 The V KICK is the most compact and versatile drum microphone in its class, intended for use with kick (bass) drums and other sources such as miking bass guitar speaker cabinets, floor toms or...

 Evans™ EQPC2 is a clear non-slip plastic bass drum patch for double-pedals, which increases attack and strengthen the head without affecting sound quality.

 Evans™ EQPC1 is a clear non-slip plastic bass drum patch which increases attack and strengthen the head without affecting sound quality.