2b second mounting facility thread class right-hand second mounting facility 3.320" overall length 3.250" overall width 32 second mounting facility thread quantity per inch unc second mounting facility thread series
2a single mounting facility thread class 0.437" single mounting facility thread length 2.591" overall length tap, circular, bushing mount unef single mounting facility thread series
2a thread class right-hand any acceptable overall length 1.500" overall width 18 thread quantity per inch box/wall mount external thread unef thread series