My old Masi is a 54cm frame. The top tube measures out to 20”. This was medium and a good secure fit. It feels solid and the machining is beautiful. Wish it came in colors but still is way better than expected. I got the sizing info from the Silca website.

Silca's sizing approach is DEFECTIVE. Their Medium size is too large for my bike frame - I compress the pump completely and it does not fit. So I ordered a small - and it falls out. It would be SOOOO easy for Silca to design even one inch of overlap in their sizing and solve this problem. But they didn't. That is an ENGINEERING FAIL.

My son got this from me as a present and he is very happy with it.

A lovely classic pump

What can you say simply sublime