Model RC Boat Complete Coupling to join a 400 Motor to M4 Threaded Propeller Shaft. This includes: 1 x 2.3mm coupling with grub screw for the 385-400 sized motor 1 x Universal joint (joins the 2 brass couplings) 1 x 4mm threaded coupling for the M4 threaded propeller shaft The coupling tightens to the motor shaft using the grub screw and threads onto the threaded propeller shaft. (Please note: Motor shown in image not included and is for display purpose only, to show suited motor)