Lug Nuts?
 

Are all lug nuts the same size? I'm asking because on discount tire, they advertise a lug kit with the purchase of a set of rims because they claim that "original equipment lug hardware will not work on aftermarket wheels."

I don't want to spend $45 on this wheel installation kit if stock lugs or bolts already work..

I bought some wheels from discount tire and they packaged a lug nut kit in mine. I think they're right though. The stock lug nuts were a bit too large to fit in the holes for the aftermarket wheels. They send a Gorilla Lug Nut kit.

So does that mean only certain lug nuts fit with certain wheels? Or do OEM lug nuts have their own special size and all aftermarket ones are universal?

Some aftermarket wheels will work with stock lug nuts. But in most cases they require specially made ones. I am surprised that wheels you chose do not come with its own set of lug nuts. Usually they sold together as a set.

I don't know what wheels you are buying but most aftermarket wheels use a tapered design which is different to OEM. You will need the correct nuts for fitting properly.

A lot wheels manufacturers sell lug nuts seperately.

Looks similar but I wouldn't risk it

Stock lug nuts are known as acorn nuts and aftermarket lugs do not have the same taper as acorn nuts. I usually only use the OEM lugs on OEM rims and use aftermarket lugs on aftermarket wheels just to avoid any issues with the lugs not being able to properly secure the wheels to the hub.