US&S HC81 8 Inch lights

[Solid Cold]

Hi guys, new to the forum. For my first message (or post I guess) I wanted to ask about the US&S HC81 8 inch light, since I recently bought a pair. Here is a video of similar lights to mine (https://www.youtube.com/watch?v=1hApI6UcnuY)

When were they made?
When did they stop making them?
How rare are they?

Thanks!

[Antarticdoof]

1 and 2. Between 1935 to the Early 1960's when the WABCO Style HC-100 replaced it.

3. Still somewhat common if you know where you're looking although their numbers have been declining for decades now. Several crossing installs from the era still have them as US&S used to dominate the crossing market in the 1940's & 1950's.