The flat head version of the "Allen" screw is for flush mounting in a hole with an 82 degree countersink. These screws should only be used in low tension applications. They have a reduced size hex socket (1/8") which can make proper tightening difficult. For this reason, we recommend always using a self-locking nut (Part No.'s AN364-3, AN365-3, MS21047-3, or MS21042-3) or Loctite (Blue) Threadlocker, Part No. LT-24221. Stocked in 10-32 size, black oxide finish only. Head diameter 3/8". All sizes are threaded the full length of the shank.