The Jamis Renegade Exploit's spec sheet confirms the bike has a 1 1/8" steerer and 31.8 handlebar like the guys said above. It would be somewhat surprising if it had something different. Along with the clamp sizes and length, the remaining variable for a stem is the angle. The stock stem is a six degree stem if you want the new one to keep the same angle. Or 84°, depending on how it's listed. (Either way, it's 6° from a right angle.)