Like prototype said, it fits over the front side of your laser ( CNI types for this one ) thats where all those extra threaded rings comes into play to fit different hosts.
If you could make a ring fit for any of your hosts and get the right threadings on it you could use it on any laser....in theory...
iirc It works as a "extra lens" over the lens from your laser, it makes the beam more thicker but it also allows you to focus your laser way further than without the expander.
If i made a mistake feel free to correct me
Anyway it seems like a verry nice deal.
@foxer
Good luck with your sale, i doubt you need it though
Darn... It's going all the way to Austria and I was right along the west coast with it.. O well... hopefully the new beam expanders show up at DL soon.