Can anybody tell me what size lug nuts are on a 2005 Ram 1500 QC 4x4?

 

9/16
5 per wheel.
Dont forget to buy some wheel locks.

 

Yep, if they are the same as the '08, then they are 9/16 - 18. I just got some from McGard (ordered them off Amazon for just over 10 bucks a set and free shipping http://www.amazon.com/gp/product/B000COS0GK) but I haven't installed them yet. The wrench that comes with your truck is a 7/8", so if you want to be able to use that, make sure you get lugs that fit. The ones from McGard are 7/8". My truck had already come with the McGard wheel locks, so I didn't get those, but I'm sure they have them as well.