5/16-18 X 8" NC Tap HS Extra Long Plug Pulley Hand Tap.
These are new old stock . Yours will come plastic encased as shown in the last picture.
DESCRIPTION
NEW High Quality 5/16-18 x 8" NC OAL 8" HSS 4 flute plug hand tap in ground thread high speed steel.
Designed for cleaning up existing threads in low tensile metals such as metals mild steel, brass, aluminum and plastic . This tap is not intended for cutting or starting new threads