It comprises mild steel U-shaped bar of circular cross section fitted with bobbins, wound with heavy gauge copper wire and the ends are ground very flat to make good magnetic contact with the iron armature. The connections of the bobbins are made to ensure that direction of winding each pole is obvious. Supplied with carrying hook, operates on 4-6 volts d.c. Supplied with keeper with hook. Length x Bar dia (mm) : 100 x 12, 150 x 12, 100 x 15, 150 x 15.