I need to know the size of the studs to replace on hub

I've never needed that information to get the right studs. If you're buying new ones, the parts store will have a listing for the correct ones. If you're going with used ones, just bang 'em out of the same model car at the salvage yard.

Be sure to use a torque wrench every time you install the lug nuts. Over-tightening is the number one cause of damaged studs. The parts store will also have a listing for the proper tightness with steel or cast wheels.

Can you take a piece of the old one to match up? I'm trying to figure out where to find the diameter. That won't be listed in the service manual.

Very often there are two different size bolt patterns with different size studs for the same car model. There's lots of differences, for example, with my '88 Grand Caravan depending on whether it has 14" or 15" wheels. Your car was available with 15" and 16" wheels. That could explain why someone looked up the wrong studs, but normally they would ask you the tire size when they see multiple listings.

Measure an old one. It's okay if the new ones are a little shorter as long as the stud peeks through the nut all the way. They can be longer too as long as the nuts don't have chrome caps.

It sounds like you're getting these from a one-size-fits-many selection. The dealer will have the exact replacements if you can wait until they're open.