Shanghai No. 4 Watch Factory 上海手表四厂 began as Tak On Clock Factory in 1932. Production of stopwatches began in 1959, and it was renamed Shanghai Stopwatch Factory in 1966. Three years later it began to manufacture the SM1A movement, which, when improved to become the SM1A-K, won the award for China's best wristwatch movement ten times.


The factory's name was changed again to Shanghai No. 4 Watch Factory in 1978 when stopwatch production was moved to Shanghai No. 2 Clock Factory (which took over the name Shanghai Stopwatch Factory). The name was changed yet again to Shanghai Diamond Watch Factory in 1986.


It did not survive the crisis of the 1980s and 1990s, and its assets were sold.


Factory codes: SB, SM