This is one case where it might be better to be more diligent. If this was a manufactured weighted bat used specifically for warmup, I'd let it go. However, it being a steel rod with a knob welded on it, I would tend to disallow it - basic reason is this, lets say the metal shop teacher did this, and lets for argument sake it fails and someone gets hurt. Everyone here is in deep sh|t. The shop teacher for fabricating, the coach for allowing it, and the umpire for not disallowing it, not to mention the school itself, and the district. I don't want any part of it. We have standards for all equipment used, including bats. There is no reason to lower the standards for convenience. Call me OOO, but that bat will not find the light of day on any field I officiate. Especially since I'm the last person in line who is or is not going to approve this for use.