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 » Other » 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 (47 RPM at 12 V) 4pcs Miniature Ball Bearing (3mm internal diameter) Passive Buzzer Module High Power PWM Switch Module (5 – 36 V, 15 A) JGB37-545 DC Gearmotor (22 RPM at 24 V)