Green’s Dictionary of Slang

stringers n.

handcuffs.

1893		Kipling ‘My Lord the Elephant’ in Many Inventions (1919) 56: The corp’ril of the gyard [...] unlocked my stringers, an’ he sez: ‘If it comes to runnin’, run for your life.’.
1906		A.H. Lewis Confessions of a Detective 99: Young Steendam, realizing fate in the guise of the steel stringers on his wrists, ceased to struggle.
1949		Monteleone Criminal Sl. (rev. edn).