Loose ..."retaining element"?

[Snoopydance]

Well I have been using a borrowed lens for my Pentax K1000 but will probably have to give it back soon (the person who owns it has a K1000, but it's broken) and the lens it came with has a little problem. It's a SMC Pentax 55mm, unlike the other which is a 50 mm, and I have no idea how to keep this front part of the lens on. It's not the glass, it's just the little ring that goes on the front with the specs for the lens and it comes out as you focus... know what I mean? I can put it back in and twist it a little and it sounds like it locks in a little or something but it still falls out no matter what. Anyway, I can't get a picture of it now but if anybody has any idea how to fix it please let me know.

Edit: I searched for a picture of a similar lens just so you'd know what I was talking about if I didn't describe it well. http://www.gadgetmiser.com/Lens%20Pe...0f2%2050mm.jpg The only part with words on it is what I'm talking about.