Looks like the main shower control and a MOEN ceramic valve, bought in any big box stores. With water off, use your Stillson wrench [compression]and turn out. The department manager can immediately match you up. Taking it home put a 2 wrap Teflon tape around the threads and replace the valve, tightly but gently. test for leaks and replace escutcheon and handle .By the way compare it on line, if you can, to be sure before you remove it.