A screw whose head has a hexagonal socket.

(UK) A hex head wrench.

plural of Allen wrench

plural of Allen key

plural of Allen bolt

plural of Allen screw

(communication theory) A graphical representation that reveals the exponential drop in frequency of communication between engineers as the distance between them increases.

plural of Allen curve

plural of Allen charge

(US, law) An instruction intended to prevent a hung jury by encouraging jurors in the minority to reconsider.