Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

The secret's out! I've been making parts for Marklin and other engines for years, and you will find, more often than not, that it's an oddball American thread that will best match what was used on pre-1930s engines from Germany. Metric is more common later. Best to have a large selection of taps and dies for both, not to mention good thread gauges.