I measured this pot at various degrees of rotation and it behaves like an linear taper pot. The "389-L" series pots feature very short locking shaft. Pot body measures .529" X .515", height of body approx. .438". Metal part of body looks like stainless steel. Pot shaft has a slot on the end for screwdriver adjustment. Three thin blades are typically soldered into a PC board bur could also be carefully bent into lugs for hard wiring. This type of pot is commonly used in calibrated electronic test gear. Guitar effects builders find them useful too; these are small enough to build into even small stop boxes. These are very high quality SEALED pots, much better than what you usually see in modern musical electronics. Clarostat pots were frequently used in military electronics, fancy test gear, scientific equipment, wherever high performance and reliability were the ticket. Probably made in Dover, New Hampshire USA, looks like '80s.
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