On AICS pattern bottom metals. I'm working on one and don't really know what spring to put in one. I'm using the spring from a clicky pen right now for testing purposes, but I need something sturdier for actual use.
From my limited experiences the typical latch spring is similar to the trigger spring or hammer spring in an AR-15. I think I have a picture of one out of an AICS. If I find it I'll post it.