welcome to the forum. Kama is indeed 2603 and all of these are 2603. The numbers you see are the serial numbers of the movements. USSR had calibers printed on some movement but not all and during some years but not always. Caliber is typically 4 digits (not always) with some letters (not always) but serial numbers are usually 5 or 6 digits. Got it?This is more of a learning question than a true Franken watch question but perhaps it fits here anyway. How do you tell Soviet movements apart?
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The three images are all from late 50's or early 60's Kamas. The three listings gave different movement numbers even though they should all be 2603 movements and to my very novice eye they look the same in general construction.
If I may add a second question; does the solid ring in the left image versus the hollow spaces with tabbed thin rings in the middle and right images indicate anything such as a non-original case?
Kamas are typically in a bayonet case with the metal spacer with round tabs is correct. Triangular tabs are normally found on early Vostok (ChChZ) watches but NOT Kamas.
I have to mention that there were small number of Kamas made NOT in bayonet cases but there is NO catalog to prove it (but there are enough good examples that such release did exist).
also, please attach better images next time because these are not really usable.