Various personal work.
I grew up around tractors, old trucks, and lots of small two-stroke-engined tools (weed whackers, lawn mowers, rotary cut-off saws, yadda yadda). When I was a teenager, my brother and I started working on old cars with our dad.
To this day, cars, engines, mechanicals, etc. are some of my favorite things to draw. In keeping with my style, I often inject a bit of fantasy into my mechanical drawings or just make up mechanicals that never existed.