Originally posted by simple1 On a non-Pentax adapter many remove it. Just keep in mind when focusing that it may rotate the adapter.
I have a couple of non-Pentax adapters. I put the adapter on the lens and leave it there, so each lens has a dedicated adapter, essentially turning it into a K-mount.
I removed the spring clip from all my adapters. I have never had a problem with the lens coming loose during focusing. They fit very snugly and normal use doesn't affect them. May impression is that they are just as secure as the M42 lens was on my Spotmatic. There was no locking mechanism on that camera or those lenses and I never had a problem with the lenses falling off or coming loose.
I know that many here swear by the OEM Pentax adapter and swear AT the non-OEM ones. Personally, I have never had a problem. As always, YMMV.