I believe you are right about 7 inch wheels. I picked up this cart and plan to clean her up, but I do have an immediate use for it and one of the wheels is losing air. I'll look into doing a patch of the innertube too, but sometimes taking apart the wheel can just result in the whole things becoming totally unusable until a replacement tube can be found.
I pulled off the offending wheel and cleaned it up so I could take some measurements and inspect it.
The wheel actually says 'Saginaw Products Corp' and has a grease zerk and bearings in it. It sounds like bushings were the norm for at least some sulkies and/or carts.
The tires are 4.10/3.5-6. So it seems that someone replaced the wheels somewhere along the line?
I tried taking it apart last night, but the tires seem to be bonded to the wheel halves. Anyone have a good trick for separating them? I was going to try a sledge and a block of wood to reduce the chance of accidentally whacking the rim.
For a 4.10 - 6 I'd just cut the sidewalls, pull the rims apart, and clean up the offending crud on the inside of the rim. Soak with what ever you want but once you get it all cleaned up, then it will come off. 4.10 - 6's aren't that expensive.