Screw threads- lots of fun here
Metric Iso
English
Whitworth
Society (Whitworth var. for microscope objectives)
Unified UTS
British Microscopical Society
Lowenhertz
Aerospace metric
Fahrradgewinde (a German standard bicycle thread)
CEI (Cycle Engineers Institute)
Hose coupling threads (various)
Etc.

And others now dropped but needed in old machinery, motorcars, etc.