Originally posted by Aaron28 not necessarily a 'latest acquisition' but a discovery of an older one...…
turns out a M42 lentar 135/f2.8 preset is T-mount....swapped out with a T to K adapter which is great as I prefer the Tmount to m42 seems more secure on camera and no risk of the problems associated with the m42 ring getting stuck on camera
however I am not convinced the proper registration distance is occurring as it focuses well past infinity which is not a deal breaker because rarely shoot infinity with a 135
I remove the spring clip from my M42 adapters, and permanently install them on the lens, using a small drop of Loctite 242 (blue) threadlocker. That way each M42 lens is made to be a permanent K mount lens. No muss, no fuss, and no stuck adapters.
(note that when I say "permanent", it isn't really, as Loctite 242 blue threadlocker is always removable, but it will keep the ring from unscrewing during normal mounting and dismounting of the lens(es) - don't use the Loctite 271 red, as it requires heat for removal, something one doesn't want on the camera mount)