Thing #19 - 3-Terminal Adjustable Regulator

I got an electrical component of some kind. Made in Japan, reference 303-179, LM317LZ. I'm not an electrical engineer type, but this website says it's a '3-Terminal Adjustable Regulator'. I'm still none the wiser. Safe to say, this particular regulator will spend an unfulfilled life, forever sealed within its little static-proof bag, tucked inside a record box, unaware what it feels like to regulate little tiny jolts of electricity for the good of humankind.

Jon, London