Specification:Aluminum alloy is light, the tip screw is 90 levels design; 45# metal hardness is high, the end screw is one hundred eighty levels design. If you prefer to aluminum coupler ,please buy Aluminum CouplingMaterial: 45# steel,hardened via warmth treatment, and then electroplatedInner Diameter:3mm,3.17mm,4mm,5mm,6mm,6.35mmCylindrical Diameter: 10mm; Cylinder Height: 10mm; Overall Height: 12mm; Fixed Hole Screw:M3Fixed Hole Distance:16mmInner Diameter:7mm,8mm,10mm,11mm,12mmCylindrical Diameter: 16mm; Cylinder Height: 10mm; Overall Height: 13mm; Fixed Hole Screw:M4Fixed Hole Distance:26mm(11mm/12mm/14mm);24mm(others)Inner Diameter:14mmCylindrical Diameter: 18mm; Cylinder Height: 10mm; Overall Height: 13mm; Fixed Hole Screw:M4Fixed Hole Distance:26mmPackage Included:Coupler x 1Spanner x 1Screw x 2