Designation S50
Bore 5/8  inch
Stroke 1 1/4 inch
Length 8 1/2 inches
Configuration Horizontal single cylinder
Extra equipment Drain cocks
Displacement lubricator
Taps required 2, 4, 5, 7 BA
3/16 x 40 tpi
1/4 x 32 tpi
Notes A nicely proportioned model of a mill engine which Stuart produced in large quantities as fully-machined kits for assembly with hand tools only. Consequently, most S50s run pretty well - be aware though that raw castings were supplied and some engines were amateur machined.

Good examples will run slowly with their long stroke configuration and are rather pleasing to watch.