The shutter blade is actuated by a crank (F), the pin of which works in a transverse slot at the top of the shutter blade. The crank is turned round by a milled head on its axis (A); on the axis is fitted a spiral spring which is wound up by turning the milled head. As the milled head is turned so the shutter blade (E) is lifted and returned, at the end of its motion it is held by a latch (B). Lifting the latch frees the spring which reverses the motion of the blade. The blade can be held in the fully open position by quickly releasing the latch.

The shutter was patented by W.L. Sarjeant and sold by W.F. Stanley.