Is this what you mean (Sonor)?
[IMG]http://i16.photobucket.com/albums/b12/vyacheslav13/th_1-12.jpg[/IMG]
If I remember right, those threaded on, or could be squeezed for "quick release". I'm not sure if they were 6 or 8mm, though.
Also, Universal Percussion used to sell "generic Sonor" ones too, although I don't see it on their website any longer. I'm not sure what the thead was on those, either. You can email Universal Percussion and ask if they have any left, or could refer you to dealers who do (www.universalpercussion.com).
If you are looking for 6mm exclusively, have you tried Camber T-Tops?
[IMG]http://i16.photobucket.com/albums/b12/vyacheslav13/th_1-13.jpg[/IMG]
They thread on like normal wing nuts, but they function like the old school "Cymbal Snaps". The good thing is, they have no moving parts like a Cymbal Snap. You just take the cymbals on and off at an angle. I use these on all my stands, and it works wonders, especially if you don't use a top felt (I don't). Even if you do, you can maniuplate a felt on and off pretty easily if you stretch the center hole a bit. They come in 6 or 8mm. And they look really cool and "old school". You can usually find them on ebay. There is a guy on ebay with the seller ID of "kikoka" that sells a lot of Camber stuff A lot of Sonor stuff too. Check those t-tops out. They have the offical Vyacheslav Seal of approval!