401 Standard Escutcheon Cup Steel - Available In Multiple Colors And Sizes - W132

Outside Diameter - 2 1/8"
Depth - 1 7/8"

Inside Diameter for 1/2" NPT Heads -  3/4"

Inside Diameter for 3/4" NPT Heads - 1"

Previously Part# E9. For use with 401 steel skirts.

NPT stands for National Pipe Thread.  To determine what size sprinkler head you have, measure the bottom of your sprinkler head at the base of the threads.  The 1/2" fire sprinkler base measures at 3/4".  The 3/4" fire sprinkler base measures at 1".