You've got a damaged bolt-maybe it's stripped, maybe it's bent-so you head to the hardware store for a replacement. There you are, surrounded by bolts, nuts, washers, and all sorts of small hardware.
Speaker 1: It might need measuring. Speaker 2: OK, no problem. (TO AUDIENCE) So I've been asked to replace this bolt that's been worn down. I'm not sure what size the bolt is, so I'll need to measure ...