Deltrol Controls is an electromechanical control manufacturer specialising in solenoids, relays and valves.
100C and 900C are series of clapper solenoids: that is, solenoids with a pivoting armature. The voltage ranges spanned by both series were given in 2011 as 6–240 V AC and 6–110 V DC. Holding forces for the 100C 24 V DC model ranged from 22–33 oz depending on temperature.
Although these are not keystroke actuation clickers, 100C solenoids have been used as such. 6 VC DC model 29376-60 was used by Cortron in keyboards, in particular:
Deltrol no longer have any details on part 29376-60, but they only have “Core Tron” as a customer of it, suggesting that it was a custom-made part designed for sound output and not actuation.