3mm to 4mm Coupling Hub Hello Customers, we would like to inform everyone that we will not be accepting orders until we fix the issue of disappearing shipping cost from your orders. We are still investigating and fixing the settings so that the correct shipping cost will be displayed in every order. Thank you very much for understanding » All Products » 3mm to 4mm Coupling Hub This copper coupler can be used for connection of 3mm to 4mm shafts of RC toys, boats and helicopters. SKU: OTH27407972788 Price: 0.99 $ Product in stock SSL Certificate Quantity Updating cart... This copper coupler can be used for connection of 3mm to 4mm shafts of RC toys, boats and helicopters. Specifications Length: 20 mm Material: Brass Related Products JA12-N30 DC Micro Gearmotor (470 RPM at 12 V) JGB37-3530 DC Gearmotor (960 RPM at 24 V) 10pcs ULN2003A Darlington Transistor Array JGA25-370RC DC Gearmotor with Extended Axis (13 RPM at 6 V) JGB37-520 DC Gearmotor (319 RPM at 24 V)