*. *The brass coupling is a through hole connecting two optical axes of different diameters, or connecting motors and an optical axis, or connecting axes of different diameters. *It can be used as either a screw rod or a transmission between the propeller shaft and the engine of a model remote control ship. *Side screw holes are unified as M3. Each coupling is supplied with four screws. *There are many children of joint couples on sold. For example "2mm to 5mm" means the apertures diameter at both ends were 2MM and 5MM respectively. Please choose the correct sizes to purchase. Specifications: *Material: brass *Diameter of both ends of cross section: 9mm *Intermediate diameter of cross section: 7mm *Total length: approx.20mm *Optional sizes: 2mm to 2mm 2mm to 2.3mm 2mm to 3mm 2mm to 3.17mm 2mm to 4mm 2mm to 5mm 2mm to 6mm 2.3mm to 2.3mm 2.3mm to 3mm 2.3mm to 4mm 3mm to 3mm 3mm to 3.17mm 3mm to 4mm 3mm to 5mm 3mm to 6mm 3.17mm to 3.17mm 3.17mm to 4mm 3.17mm to 5mm 4mm to 4mm 4mm to 5mm 4mm to 6mm 5mm to 5mm 5mm to 6mm 6mm to 6mm Package Contents: 1 x brass coupling 4 x screws 1 x wrench