3a thread class right-hand 0.589" thread length 14 thread quantity per inch internal thd 2.500-28 with locking feature passivate surface treated serrated unc thread series
2a thread class right-hand 0.418" thread length flat countersunk head style 80 thread quantity per inch cadmium screw surface treated unf thread series
flush (flat) countersunk (included angle - less than 135 deg w or w/o chamfer) head style 0.188" grip length ns" letters after the material code "b" indicate no preference to lock type (may be visible or internal) . rivets with no letter code (indicating visible lock type) passivate surface treated