I had that problem! Took twelve years to sort. My tap is easily over 40 and may date from 1910. The diameter of the threaded end was 22mm approx and nearest imperial measure seemed to be 3/4". I bought a few 3/4" connectors: hozelock et al., all were marginally too small. Others were too big. I found a post on Jim's homebrew website that suggested trying 5/8" even though that did not appear to be the correct measure! It works; whoopee! I now have a 5/8" brass fitting which I got online from McNeill DIY. It cost the same as a new tap because of p&p on top, but having read your reviews of new taps :-( I decided to stick with the antique one (and much easier to fit a connector than a new tap). McNeill's rang me to discuss my problem, very nice, and the connector arrived in 3 days, which was two days faster than the date they gave me. Happy happy happy.