A Socket set screws is also known as a Grub screw. It has no head, the length is measured overall and are fastened using a hexagonal wrench also known as an Allen key. These have a Knurled Cup Point end and are used for quick and permanent location of gears, collars, pulleys or knobs on shafts. They resist most severe vibration. These are made of the highest tensile available. Use Allen key size = 8.0mm