I had this problem myself a while ago. I don't know about your new pots specifically, but I think the problem is that some factories make them to imperial sizes and some to metric. (Generally if the pots were intended for a European supplier, they'll be metric, if US then imperial, but that's not necessarily true in every case.)
I believe most pot shafts are either 1/4" or 6 mm...so whichever you've just put in, I'd guess your old knobs were the other!
Edit: according to google, 1/4" = 6.35 mm. So I guess you must have had 6 mm pots in there originally, and you need a set of 1/4" knobs. Surprised to hear you're having trouble finding those stateside, I must say!
Brandoni / self-build Precision; Epiphone EB-3 SG Bass; Schecter Model T; one Frankenbass
#136 British Bassist Club
Last edited by AuntieBeeb : 02-01-2013 at 04:58 AM.