After this discussion on duals and measuring / photographing my spool extensions for readers, I decided to contact Yanmar themselves and ask about the original intended use of the extensions. I have never actually been able to figure out if they were meant for duals or simply as an extension. (I have been told both by many different people through the years). Since I own a North American YM240D and provided my serial number, they were very helpful in offering the following information concerning this original, optional equipment for the YM240D:
An engineer at Yanmar confirmed these were manufactured as axle extensions and were not actually designed for dual wheel application. They were meant to extend the axle for tractor stability and told the YM240D was engineered to use them where needed.
While the YM240D did not originally come with ROPS, it was also confirmed that a catastrophic failure of an axle would result in a flop or roll over. They encouraged anyone with any Yanmar tractor (not just a 240) to add ROPS if not originally equipped with it (after experiencing a roll over, I didn't need the encouragement). They were not aware of these extensions resulting in failures but did acknowledge they create additional (engineered for) stress on axles.
Don't know if this is of any interest to anyone else, but thought since they actually got back to me it would be worthwhile to post a Yanmar opinion on this.
