pack of 6-Screw Mandrel 1/8" Diameter Shank-1/8" Screw-Large Head-Nickel Plated Steel

This is called the "Hippie" head mandrel because of the relatively large 8mm outside diameter of the screw. Use this large headed mandrel with larger wheels. The diameter of the threaded part of the screw is the the larger 1/8".

The diameter of the shank (the part that goes into your handpiece) is 1/8" (3.18 mm)