Wiper problem

[pappaecho]

My Princess 33 came to me with three speed wipers made in China. On Tuesday the helm side unit burnt out in a force 7.
In a spare locker there are two "old" single speed wiper units which fit the boat, and which work. What is puzzling me is that the end spigot onto which the wiper arm would fit is a 3/8 inch stainless shaft. No splines or anything onto which to attach a wiper arm. I assume that some sort of cap fitting would be attached to the spigot, and the wiper arm fitted to the cap, but there is nothing else to how how it was done. The makers name is ROCA
Anybody any ideas???

 

[sarabande]

I guess they are similar to the Landrover wiper arms,; there's a dimple on the arm, and you have to locate the wiper blade and wind in a fixing screw.