Old Metric Propeller Hub For Wood Propeller

 With the OX-5 Engines were 2 propeller hubs for wooden propellers.  This one is complete except for needing to be re-plated with Nickle plating.  It is also in serviceable condition. It was completely orange with rust when I stared.  It cleaned up nicely in the Electrolytic de-rusting bucket. It's the rusty one at the top.

The more amazing thing, when I started measuring it, was it's Metric not English.  It fits a tapered shaft with a 10 mm key.  There are 2 sets of 8 bolt holes for 10 mm bolts.  The inner set is 110 mm on centers and the outer is 120 mm on centers.  The propeller would have been 90 mm thick with a 60 mm hole. The outside diameter of the hub and of the plate is 150 mm.

 The front plate is splined to the hub with 4 10 mm splines.  Modern (1930's +) light plane hubs do not attach the front plate to the hub. The hub is held to the shaft with a nut which is threaded to the hub and to the shaft.  This nut is held in place with a clip which is locked by safety wire around it in the gap between the hub and nut.

The nut outside, hub to nut, thread is 50 mm diameter with 1.25 mm pitch threads.

The nut inside, shaft to nut, thread is 40 mm diameter with 1.25 mm pitch threads.

There are areas which either still have plating or the plating was still protecting the base metal before derusting.

The back of the hub is stamped with a (part number ?) 150 and below it, around the flange to the bottom, with the symbol for Omega.  There is also what appears to be a QC acceptance stamp near one of the inner bolt holes.  The front plate is stamped the same but the number is 151.

The million dollar question is what engine does this fit?  Any help out there?