The Omega caliber 571 is a Swiss made automatic movement with 24 jewels and adjusted in two positions. This movement was first introduced in 1958 and was used in Unishell Seamaster watches into the 1960s. “Unishell” indicates that the case opens on the dial side.
Omega 571 VS 570
There is a similar Omega caliber 570 which, according to Omega, was also introduced in 1958. The caliber 571 has 24 jewels and the 570 has 17. Many watches that were imported to USA back then featured 17 jewels because anything over that would incur additional customs charges. This would also explain the “OXG” stamp to the right of the swan neck regulator in the picture above. OXG is one of the 3 letter import codes found on many raw Omega movements (cased by Norman Morris) that were intended for the American market.