I have two sets of MAFAC Criterium brakes, but the two bolts that hold the springs and the arms down are all rusted. Does anyone know of a good, durable solution to replace them? I'm not well at home in the fastener business and I'm not all that for buying a thread gauge, so is there anyone who can fill me in on the details? I'm not particularly looking for a bolt that looks the same, and especially not for original spares, seeing how bad the original chrome is.

For a calliper I purchased a couple stainless steel M6 bolts at the Praxis (store). I filed the lettering away and polished them up. Looks quite good. Not exactly identical to the original, but it is tidy.

Oops sorry, above was my treatment with a Weinmann calliper

Thanks Mel! I'll try those.

They show up on eBay once in a while.

The bolts are M6. Get some stainless bolts (~20mm) and appropriate washers from your hardware store or online until you source originals.

thanks for confirming that the bolts are M6. My aim is not to find NOS ones, since my purpose is (as I think I stated in the OP) to upgrade the MAFACs. Originality is not the point, since they're to be paired anyway to some ergopower levers on a retromod build (with fenders!).

If you were in the US, I would recommend McMaster-Carr. I could mail you stuff from there if you like, but I bet M6 bolts are easier to come by in Yurp than they are here.