Green’s Dictionary of Slang

screw n.3

[Afk. abskroef, screws; ? i.e. they are part of something larger]

(S.Afr. township) a minor criminal gang.

[SA]C. Glaser Bo-Tsotsi 49: Small-time, petty criminal gangs, known as aboskroef [sic] (‘screws’), or bigger-time criminal gangs ‘schemes’. The small-time, generally younger, ‘screws’ aspire to become ’schemes’.