Helicopter Dual Tachometer Kollsman 981BX-8-023 H-21 Piasecki F-104 but also on the US

but also on the US Army Air Corps' UC-43 Beech Staggerwing (see photo from flight manual dated 1944)

and the markings are of both the classic Munsell green and white as used on US Navy aircraft instruments of the era

It is in superb condition given its age

One has a service date of 1973 stamped on its side

it would seem to be for a dive bomber

Helicopter Dual Tachometer Kollsman 981BX-8-023 H-21 Piasecki F-104 but also on the USHere is a dual Tachometer for use in military helicopters, indicating RPM for the rotor on the inner scale and rotor for the outer scale with a ratio of 9. 7: 1. The pointers will be aligned once the rotors are fully engaged. It has a serial # prefix of AF57, likely indicating manufacture date of 1957 for the US Air Force. It was used in the H 21 Shawnee Workhorse Piasecki Helicopter, as confirmed in its parts list dated 1957. See photo of cockpit