Features: 100% brand new and high quality. These couplers can connect motor shaft and hex wheel. Made of premium brass material, it is durable and has long service life. There are 4 pieces of couplers in one set that you can use for your DIY project. Widely used for connecting toy cars, robots, etc. Specification: Material: Brass Inner Hole Diameter: 2mm, 3.17mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm (Optional) Screw Hole Size: M4 Quantity: 4pcs Weight: 47g~60g / 1.7oz~2.1oz (approx.) Package list: 4 * Couplers Package List 1100% brand new and high quality. 2These couplers can connect motor shaft and hex wheel. 3Made of premium brass material, it is durable and has long service life. 4There are 4 pieces of couplers in one set that you can use for your DIY project. 5Widely used for connecting toy cars, robots, etc.