1cres per ams5610, immunize per bendex specification no. Es-091, 26 to 33 hardness rating, rockwell c scale, 1.52 in. O/a lg, 0.2770 in. Min, 0.2785 in. Max head dia, 1/4-28 unf thd modified per bendix specification no. Es-0431, 0.2196 in. Min, 0.2218 in. Max pitch dia