Zenit's unmetered Soviet M42 SLR — the B, cloth shutter, fully mechanical, 1968.
The Zenit-B is a 35mm film SLR made in the Soviet Union by KMZ from the late 1960s, essentially a Zenit-E without the built-in meter. It was an even more basic and cheaper version of the widely exported Zenit line, sold as a simple, unmetered budget SLR through the UK and other markets.
It is an M42 screw-mount SLR with a horizontal-travel cloth focal-plane shutter offering a limited speed range, typically around 1/30 to 1/500 plus B. Unlike the E it has no built-in meter, so exposure is set fully manually using a separate meter or judgement. The shutter is entirely mechanical and works without any battery, and many examples lack an instant-return mirror.
The Zenit-B suits students, beginners and users wanting the cheapest possible battery-free mechanical SLR to learn exposure on with a handheld meter. It is heavy and plainly built, and the limited shutter range, absence of any meter and non-instant-return mirror on many bodies are the expected limitations of this very basic design.
On the used market, Soviet build quality varied between samples, so inspect each body on its own merits. With no meter to test, concentrate on the mechanics: run the shutter across its speeds watching for capping and inaccurate timing, inspect any light seals and dampers for perishing, and check the prism and focusing screen. Test the film advance and rewind feel, and expect sample-to-sample variance, so examine carefully before buying.