Tips: If you wish different specifications of copper gears, you could touch us. Calculation approach to equipment outer diameter: gear diameter = (number of enamel + 2) * modulusFor example(0.4Modulus 10T): Gear diameter= (10+2)*0.4=4.8mm Specification: Inner hole: many non-compulsory Material: Brass Practical handheld remote control aircraft, RC Car model, Gear Box etc 7T Gear thickness :3.6mm Other gear thickness:4mm Package Include: Gear x 1pc