It's hard to imagine a Columbus SL frame having a stamped rear dropout with double eyelets and requiring a derailleur with claw hanger.
Originally Posted by
RJMurphy
...And I don't have a caliper to measure the seat stem (which has no marking at the head), and I must be an idiot because with a string and tape I get approx. 8.5 cm diam. That can't be right....
To measure the post more accurately without calipers, cut a 5mm by 100mm strip of paper. Wrap it tightly around a cleaned section of the post and mark the paper where it overlaps, using a sharp pencil. Remove the paper and measure from the end to the mark. Divide the measurement by 3.14 to get the diameter. Repeat the process to ensure accuracy.
Check the bottom bracket cups for thread standard stampings.