They don’t make — or package — them like they used to. This is a vintage radio crystal from the Bliley Electric Company. Bliley is still around, making modern oscillators and even space flight hardware, but this vintage unit is a beauty.
Introduced in the 1930’s, the Bliley LD2 was a popular frequency standard for amateur radio operators. A 1935 advertisement in QST magazine claimed efficiency and extremely low drift (<8 ppm/°C), guaranteed operation, an improved holder, and a cost of only $4.80, or $82.79 in 2014 dollars. This particular unit is calibrated at 3.9895 MHz (“3989.5 KC”), for a radio wavelength of about 75.2 m.
Unlike most modern crystals, this type comes apart easily. Inside, two rectangular steel plates sandwich a thin slice of quartz crystal, all held pressed together with a simple spring.
If you’re interested to learn more, there’s a wealth of additional information about vintage crystals and the Bliley company available online, here.