Oliver Hart Parr 70 odd rear steel wheels

[53 IH Garand]

I recently bought a 1936 Hart Parr 70 and a bunch of misc. parts on an auction, and was curious about 2 sets of Oliver tip-toe steel that I bought. The first set seems like the standard Oliver steel, the center support ring looks like a wagon wheel with rounded edges and 2 3/4" wide marked "BA705" on the center casting. The other set though is different. It looks the same at first glance, same design and all. But after closer inspection the center ring is only 1 1/5 wide and more of a straighter edge, more purpose built than the other type. This thinner ring also makes the long bars bend sharper and about 2" farther away towards the outer lug ring, which is also a wider heavier ring itself than the other set. The center casting is almost the same, same design and all, but more of a round faced than the other set that are straighter faced. This casting is marked "BC705". I was wondering about these differences, if anybody could help that would be great. If pictures would be needed I can work on it. Thanks, C. Scott.
 

[J. Schwiebert]

Back in those days Oliver had a pretty simple parts system. 705 was the part number for the wheel. The first letter identified which tractor the part was first used on B being the letter for a 70 and in particular a rowcrop 70. As parts were improved a second letter was added. In other words BA meant it was improved from the first design. Since BC is later than BA it superceeded the BA part number. Does that help to start with?
 

[53 IH Garand]

Thank you, that helps. More of an IH person so Oliver numbers seem a bit foreign. It seems like I see a lot more of the BA705 types, though I could be wrong. but the center ring seems like more of a step backwards but maybe they had problems with the other type.