There are numerous versions of the Leica M3, and over time, many people have shared their experiences with them. Some enthusiasts have even published books on the subject. However, there are sometimes discrepancies in how people differentiate between the various models, and I have personally encountered versions that are not covered in their collective experiences. With so many versions available, it can be challenging to determine which information is accurate. Nevertheless, the identifying features of these models still serve as useful reference points.
Leica M3 single-stroke and double-stroke models have distinctive serial number features.
1） Boundary between single-stroke and double-stroke models. Leica M3 cameras with serial number 919251 and later were produced as single-stroke models, whereas earlier models were double-stroke. The lever on the double-stroke models is shorter than that of the single-stroke models. Early Leica M3 cameras had a single red dot in the center of the film rewind knob, which was primarily found on single-stroke bodies. Later on, the film rewind knob was modified to include two red dots and can be found on both single-stroke and double-stroke models.
2）Depth-of-field preview diagram. The Leica M3 single-stroke version’s viewfinder is equipped with a depth-of-field preview diagram, which is indicated by two raised bumps located above and below the center focusing spot. These bumps represent the depth of field at f/16 and f/5.6 （50mm lens）, respectively, and any overlapping images within this range can be viewed clearly.
