Constructed from 17-4 PH stainless steel. The R45 will find itself at home on a wide variety of firearms and calibers. The robust design allows it to be used on calibers ranging from .17HMR all the way up to the legendary .45-70 Government. The R45 ships with a 5/8-24″ HUB Direct Thread Mount and ships with (1) YHM-2007 and (1) YHM-2146. The R45 accepts their full lineup of 1.375″-24 HUB mounting options.