This is a coaxial adapter, with 50 W impedance, from GR-874 to BNC male connector, made by General Radio, USA in the years 70's (vintage). The adapter is new, never used, in its original small plastic box, and was bought as an accessory of a Tektronix scope (Tektronix P/N 017-0064-00, Figs. 1 - 3). From the GR catalog it is rated from DC to 8.5 GHz frequency, admits a peak input voltage up to 500 V, and an average power of up to 5 kW into 50 W load, from DC to 500 kHz. For a higher frequency f, the maximum average power decreases as 1/f^1/2 to 0.1 kW at f = 1 GHz. Intended for use in high frequency or short pulse signals in an electronics or physics laboratory, or as a collectible item on history of electronics.