From the PacNor site on pre fit barrels.
The prefit barrel comes to you completely contoured, polished, handlapped, threaded, chambered, & crowned with a short thread shank to be set back for proper head space: ready for you to have fitted to your action. (All prefit barrels should be fitted and headspaced only by a qualified and competent gunsmith.)
This is not truly prefit like you can do for a Savage. You need a lathe and gauges to install. A home user can't just thread it on and go shooting.
Keep in mind these are production fits. No where near the precision you get with one custom cut for your own action.