That is a prop speed reduction system used to mate a propeller to a gasoline engine and slow the prop speed down. The small flange with the little bar bolted across is the propeller mounting flange. The other side is the flywheel for the engine and bolts to the crankshaft. These are used in ultralight aircraft, expiremental aircraft and even air boats used in the swamps. The RPM output of an engine is wayyyyyyy to fast for a prop and the centrifugal force would cause the prop to self destruct and disintegrate. Their are literally a bazillion different kinds of these belt reduction units made. Each unit is made for a specific engine and aircraft. From the photos you posted, the small flywheel indicates it most likely bolts to a Subaru engine. The manufacturer will be unknown because of the experimental classification and the part does not have to have an airworthiness certificate. It look like an early Foxcon open style that was used in several different experimental home build kits. I've attached a link to a kitplane sight with lots of photos and you can see these bolted to the front of the engine and also the props bolted to the flange mentioned earlier. If it's for sale I would be interested in it for one of my builds I am working on. 806-893-5371 if you have any questions

That is a prop speed reduction system used to mate a propeller to a gasoline engine and slow the prop speed down. The small flange with the little bar bolted across is the propeller mounting flange. The other side is the flywheel for the engine and bolts to the crankshaft. These are used in ultralight aircraft, expiremental aircraft and even air boats used in the swamps. The RPM output of an engine is wayyyyyyy to fast for a prop and the centrifugal force would cause the prop to self destruct and disintegrate. Their are literally a bazillion different kinds of these belt reduction units made. Each unit is made for a specific engine and aircraft. From the photos you posted, the small flywheel indicates it most likely bolts to a Subaru engine. The manufacturer will be unknown because of the experimental classification and the part does not have to have an airworthiness certificate. It look like an early Foxcon open style that was used in several different experimental home build kits. I've attached a link to a kitplane sight with lots of photos and you can see these bolted to the front of the engine and also the props bolted to the flange mentioned earlier. If it's for sale I would be interested in it for one of my builds I am working on. 806-893-5371 if you have any questions

References:

https://www.kitplanes.com/subaru-sonerai/