The Shanghai caliber SS1K (also written as SS-1K) is a 17 jewels (17 zuan) manual wind mechanical movement. It is based off of the original Shanghai caliber A581 (which evolved into the A611). This caliber was introduced in circa 1972 and produced until 1975.
There will be two letters above the caliber number. This is the date code for when the movement was manufactured.
Shanghai Caliber SS1K vs SS1 (SS1A)
The SS1K beats at a higher 21,600 bph vs the SS1/SS1A beating at 18,000 bph. The SS1K also has a larger balance wheel.