Originally Posted by OLDYELLR

When a frame is first built by the frame builder or factory, the BB shell needs to be faced and have the threads chased. The steering head also needs to be squared and reamed. Maybe even the seat tube. Most over-the-counter mass produced frames didn't have this done to save cost and it was up to the bike shop that built the bike to do it. That's probably why it says to do it in the instructions.