Having a clean out in my workshop and came across a little steam engine I built many, many years ago, it is a 1/2" Bore single acting slide valve.
I made this engine as a first project when I had a small Perris lathe, the drawing for the engine was in a book titled Scale Model Ships Their Engines and Constrution no castings were needed and it was a ideal first time project. I had the engine in a model boat at the time and it worked a treat.