The Leica M3, introduced in 1954, launched the M bayonet mount and remains for many the definitive rangefinder camera; over 220,000 were built to 1966, more than any other M film body.
It has the highest-magnification finder of any M at 0.91x with automatically selected framelines for 50, 90 and 135mm, a mechanical cloth shutter 1s-1/1000s, and no light meter. Early bodies wind with two strokes (Double Stroke); from 1958 a single stroke sufficed.
The 0.91x finder makes it the best M ever made for 50mm lenses, with an effective rangefinder base unmatched by later bodies - the reason M3s remain user cameras seventy years on rather than shelf queens. Wide lenses need external finders.
Condition drives everything: check rangefinder patch contrast, shutter accuracy at slow speeds, curtain pinholes and finder haze. Double Stroke early examples and low serial numbers attract collectors, while clean late single-stroke bodies are the practical user pick.