Did somebody say trains?
Kinda hard to collect them though.
I will go out on a limb and propose we all love mechanical things... seems to be a common thread here... not too surprising that we all (mostly) love cars, motorcycles, mechanical watches, boats, airplanes, etc.
Whereas I can't afford to own a airplane or boat I do love going to air and boat shows... even guns for me (only own three for home defense) I'm fascinated with the way they work.