So we can all be on the same page, we're talking about your 1965 bus, right? It has 10 lug rear hubs and Motor Wheels (the 1967 would have 6-lug Budd Wheels).
You ordered new lug studs Dorman 610-0159.10 which are the same as GM 3765876 (11/16-16 x 3-1/4" long studs), you got the wrong part Dayton p/n 13-1617L (1-1/8"-16 x 3.56" long), so there's no issue there, the vendor just needs to fix that for you.
My question is why are you changing the studs to begin with? If I'm reading my books right the Dorman studs you ordered should be the same as the factory studs you have now...
Steel 20" Motor Wheels and steel 22.5" Motor Wheels should swap back and forth all day, what am I missing?
Mike B
