Not sure what it fits $25 plus shipping

Looks very similar to a single six ruger 22 mag. cylinder.

Good deal bump

I just looked at my Ruger 22 Mag. cylinder and am relatively sure it is not for the .22 Ruger. CM

here are 2 Ruger S6 cylinders ... old & newer (pictured below)

OP's cylinder has a stamp and 3 letter initials which leads me to believe it's from an imported pistol.

also cylinder FS does not have the case rim milled like other cylinders

I think it fits this:

22 MAGNUM CALIBER ITALIAN FIE REVOLVER PISTOL CYLINDER MARKED PSF

I found a picture of one like it and that's what they claimed it fit.

https://thumbs.worthpoint.com/zoom/...e_1_212d0ea75af1ee82be1a544d20647008.jpg

Looks like heritage rough rider. Sharp, swept up parts the pawl grabs

based on the proof marks, further i-net research indicates cylinder is likely from a Tanfoglio Model TA22

Armi F.LLI tanfoglio Gardone, V.T.Italy model-TA22 .22-LR with the extra .22-magnum cylinder ....This revolver is imported by Excam Inc., of Hialeah, Fla.

www pics of the same/similar cylinder (proof marks are from Italian maker in 1950's)

link with other cylinder pics & origin of proof marks

https://www.firearmstalk.com/threads/22mag-revolver-cylinder-need-help-identifying.130576/page-2

same firearm FS with pics - https://www.gunauction.com/buy/14447224

I believe the fellows that said it fits an Italian pistol are correct.

I have a Heritage Rough Rider and the teeth? on the back of the cylinder that the pawl grabs are made different. The one in the OP's pic are kinda flat and turn up real quick. One side is almost the same as the other, not quite, but pretty close. The Heritage starts up immediately at a slope and then drops off, for the pawl to grab. That's the difference I see on my .22lr cylinder. I dont have the 22mag cylinder.

thank you all for the research on it, it is still for sale !