This is a "C" Check Valve for the old style (Part# 15556) Valve Block. These are quickly becoming OBSOLETE since Meyer discontinued the E-47, E-57, and E-60 units recently, not sure when Meyer will run out of these. Get them while you can. These will not work on any other angle blocks! The angle block these are for was standard in the 1970's. I had two 1979 E-47 units in for a rebuild last month, one had this old style block, and one had the newer style block. We stock many parts for the old style block as well as all parts for the new style block. Here is a diagram of the old style block for reference.