Originally posted by stevebrot Mount adapter to lens and then lens to the camera. That will take care of the fiddly business of putting the adapter into the mount opening. As for looseness, the above comments are correct. The Pentax-brand adapter should be slightly loose with a few degrees of play when mounted alone to the camera. This is by design. When a lens is mounted the back flange of the lens should engage the surface of the body's mount flange to provide proper registration to the sensor plane. It should also "snug up" the adapter onto its bayonet "ears".
As mentioned above, there are a number of vintage and FSU (former Soviet Union) lenses that have an unusually narrow back flange. The result is that the lens wobbles somewhat. vonBaloney's solution is one of the best I have read though care should be taken to make sure that there is no stand-off between the lens back and the K-mount flange on the camera.
Steve
(...lucky to be relatively wobble free with my adapted lenses...)
While my solution "works" in that in provides good friction (but no lock since I've removed the spring from the generic adapter), I'm not totally sold on the wisdom of it because basically what you end up with is a rubber washer sliding across all your electrical contacts and other mount parts, possibly rubbing off tiny bits of the washer into your contacts. So, at your own risk an all that. Also, once the washer has been on there a while and stretches out (it is basically too small at first and you force it up and hold it on with the adapter), you can't adjust it all and must be careful not to flip it backwards off the mount (or it will just fall off) -- you'll never get back your good fit and friction once it is all stretched out. A fancier version of what I've done would glue something on there permanently, but with my version if something goes wrong I can rip it off in seconds and I'm back to plain m42. If you don't mind losing infinity, the non-infinity adapters are a much easier solution to gain a solid mount.
Here is a picture of what my Meyer/Pentacons look like with the washer mount, along with a washer I haven't used yet. (Good to have a spare.) You see how the washer rests at an angle on the tapered part of the lens with inner edge down to provide the extra friction. You know I also just remembered that with these tapered mounts if you don't have the washer there, there is actually a light leak from where the spring was in the m42 adapter. So you need it for that too.