The Industar-50 is a lens with quite a long history. Its production started in the early 1950s by KMZ (Krasnogorsk) but was continued by LZOS (Lytkarino). These Tessar-design collapsible lenses were made mainly for the Zorki-5 and -6. In the late 1950s, there also appeared a very popular rigid version of the Industar-50 for RF and pancake versions for the M39 Zenit SLR cameras. The Industar-50-2 is a pancake-type lens for M42 and appeared earlier in my blog.
The lens that I present here is a collapsible Industar-50 made in Kazan. Like its "Made in Kazan" Industar-22 brethren, it's not very common.
Princelle lists this lens as Kz20.
Aperture range: f/3.5-f/16
Minimum focussing distance: 1m
Aperture blades: 10
The serial is engraved on the rear. I don't know how many versions there exist of this lens. Perhaps the serial for lenses made in 1960 also start with 60xxxx, like for the Kazan Industar-22? So far, I've only seen 4-digit serial numbers. This lens has serial number 6500. Also interesting to note is the П-mark, which is in black instead of the usual red.