Making a moving prop stick to a surface on collision

[GaleTheHusky]

I've been making a simple SWEP, and one of the things I can't figure out is how to make a prop stick to a wall/floor/prop etc. when it collides with it. I've found it once before a couple of years back on this site, but now I can't find it.

Also, don't post "use the search feature" because for some reason, I get an "Insufficient Privileges" page. I've used it already with this account, so I know I've activated it.