BRODAK Prop Shaft Extension 1/4-28 to 1/4-28 Thread x 3/42” Long Our lightweight compact spool with special nut and washer design fits onto your prop shaft to move the propeller forward 1/2" for better aerodynamics. This fits all 1/4 - 28 shafts including Brodak 25 & 40 engines. Package includes: (1) Prop Washer, (1) Shaft Nut and (1) Spacer 1/2" L. Drill is 21/64