I asked the same question on another russian camera list and got this answer from Matt -
[Use a 3/8" to 1/4" adapter, there are two kinds available, one is
like a bushing, the other has an external knurled knob. I've come to
prefer the bushing type as a permanent leave-in becuase it allows the
full base of the camera to rest on the tripod mount (particularly
important with heavy cameras like Kiev-60 and 88). I just got a
couple off ebay recently from seller rxnash, you can get them in
10-packs from camerastore.com or elsewhere... they're pretty cheap, and pretty useful!]
Garry