2a thread class right-hand 0.495" thread length pan no. 2 head style 32 thread quantity per inch navy special project passivate surface treated unf thread series
Used on F-15I. 2a thread class right-hand 0.240" thread length pan head style 40 thread quantity per inch altered item from MS51957-20, item is threaded under head 0.240 in., unthreaded portion past the threaded part is 0.640 in. passivate surface treated unc thread series
3a thread class right-hand 0.363" thread length flat countersunk head style 32 thread quantity per inch cadmium or chromate surface treated unjf thread series