Here's something I found at the local Hobby Lobby (no affiliation or selling BS) that may be of use to detailing engine houses, mines, sawmills, flat car loads, and whatever you can think of. Gears, gears, gears...these are made of what looks like laser cut wood but when painted rust, etc. and maybe some "steel" dry brushed on the teeth, they would look really nice. Very expensive at $2.99 for a bag of 36-6 styles. I can think of many things to do with these besides getting them lost in a box somewhere. You can see the approx. sizes, the trains behind are On20, they would work as large gears in N or HO, sorta large in 1:48 or so, medium in 1:35 maybe, and nice for large scales.
The scale may also be deduced (25 cent word) from the figure at lower left.
Pretty cool, I would say, and I saw some brass & steel gears not quite like these but costing more in the jewelry section at the same store.
It pays to look around...you just never know.