Need help identifying 3 handle shower diverter and how to remove it

There is a standard purpose designed socket for removing valve stems and diverter stems. It slips over the outer part and engages the wrenching flats on the stem. Shower valve stem removal socket

There are holes to use a screwdriver to turn the socket, but I have found that if the stem is balky what works best is a large Crescent wrench on the outside of the socket held close to the wall.