Originally Posted by
merziac
Its chrome steel Schwinn branded original, it had an older not original open nose Brooks Pro with Brooks clamp that is rock solid, I put a couple hundred miles on it before I changed it.
A 15mm is sloppy on it, pretty sure its Whitworth or BS, maybe just poorly sized, I have several very good Cresent's that work good to get a good bite that I used on the 58 but they are at their limit on this. I'm a lifelong tech/mechanic and have more tools than sense including dozens of wrench's, none are a proper fit so far.
I had not known Schwinn had own seatpost in 1958, that is quite interesting.
Only way I know to find a Whitworth (or maybe it’s British Standard) that fits on a saddle clamp is to use an old Raleigh flat wrench. Which is better than nothing but too short and too sharp to do the job well. Good excuse to get a bigger Crescent. Or just get an Ideale 3. One of those would look good on this build. (Eddy Merckx used one, with wingnuts, so he could adjust saddle angle on the fly.)