Years ago, I made the newbie mistake of forcing a rack screw into a steel braze-on. I had to replace that fork. And I've heard this advice many times: When putting a screw into a braze-on, put a little lube on the screw to keep rust from forming. So I take good care of rack screws and braze-ons now.
I was putting fenders and racks back on a bike today, and I had finished cleaning the screws and eyelets. When I reached into my tool bag for some lube, I realized I had regular bike lube as well as polylube. (That's the goopy stuff you use for seatposts.)
I tried polylube on a pair of 5mm screws and regular lube on a set of 4mm screws. Over time, I'll see which set of threads is cleaner, or if there's any difference at all.
I'm using Parktool Polylube 1000 and Prolink Chainlube (regular lube, not wax).
My question: Is there a difference between using regular bike lube and polylube to lubricate threads? Can polylube be harmful in this context? Or should I be using something else entirely?