This is a vintage pair of RCA 2A3 vacuum tubes. These particular examples, dated 304 (1953) are best suited for vintage amps and high end audio gear (i.e. Western Electric, Altec, National).
These RCA 2A3 Black Plate Tubes were pulled from a working 1930’s National/Dobro amp used for lap steel. They are marked “Made in USA 304, RCA Radiotron Electron Tube”. They are working, although I do not have a way to test them other than the amp they came from, which sounds great! One of the tubes has a small rattle in the bottom, though does not seem to affect the performance of the tube.