SODIAL(R) 58 styles Plastic Gears Cog Wheels All The Module 0.5 Robot Parts DIY Necessary, Model: A - Means tight Match(will small 0.05mm than standard) B - Means loose Match(will larger 0.05mm than Standard) Gear Diameter : (Teeth +2) * modulus = Diameter of Gear Modulus: 0.5 Aperture 1.5/2/2.5/3