Allen Screws - Socket Screw or Cap Screws also known as Allen Bolt or Allen Screws or Hexagon Socket Screw. Allen Screw Plugs Chrome Allen Screw Caps Stainless Steel Socket, Countersunk Socket, Stainless Steel Button Head. They are ideal as a nice looking alternative to hex set or pan head screws, for example on a crankcase side or a flywheel cowling. Also they may deter the casual thief as any screw can be undone with a screwdriver or adjustable spanner whereas not everyone carries Allen keys around. The length refers to the length of the threaded section only. The other size is the thread size NOT the size of the Allen key for adjusting it.