SPI brand groove checking rod for measuring depth and width of grooves and recesses. Back end has been ground to a point. Can be used by itself, setting the cap, then measuring with another tool, but is best used with a depth micrometer base. Fits Scherr-Tomiko and Craftsman depth micrometers. It has a 18 dia. rod with .281 cap thread dia. Phone number is a Utah cell, but I am located in Tupelo.