I'm finishing up the rear brakes on my 88 F250. Its got the 10.25 rear semi floating and the drums won't slide over my wheel studs! They are Wearever YH140397 from Advance Auto and have 1/2 holes and it looks like my old ones are 9/16 studs? Whats going on here???

 

Looks like they gave you the wrong drums!!
Advance shows several drums for the f-250, I would guess the kid on the computer didn't ask the right questions and guessed wrong..

 

I checked online and its the right part number. What other 8 lug axle has 1/2" studs? They look identicle to my old one besides the stud holes being too small.

 

I'd say they were machined wrong, probably a batch of them got through quality control.

 

I work in a garage, and it is not uncommon for parts to be put in the wrong box with wrong part # Happens a lot actually...