I believe it is justified in saying that this manufactured product, of a ball & pin universal, leaves a great deal to be desired! This simple two part mechanical design is a constant velocity joint, which when properly machined, will provide reliable transfer of the engine's torque & the propeller's thrust . All male & female pieces shown are made of AISI-O1 tool steel. All the pieces in the photos are interchangeable, have a total indicator runout of .0005", have full hard bearing surfaces & have very high wear resistance. The male ball ends are precision machined with a form tool or a convex radius tool. The balls & their 1/4'' necks are hardened, then tempered to a spring temper. The full hard M-2 steel drive pins are pressed into the balls with a .001" press fit. The female slotted ends are fully hardened only in the areas where the drive pins ride. I also adapted the ball ends to fit on the engines flywheel of both my gas & nitro engines. The small washers provide a hardened surface for the ball ends to ride against when the propellers thrust is driven up into the engines bearings. A splined set screw (Bristol Screw) with a machined point & a machined cavity in the shafts prevented any failures in these areas.
Jim Allen