Westclox kept changing their winding ratchet mechanism. The first four types listed here engage with projections pressed out of the body of the mainwheel.
Alarm Click 1: Spring click riveted outside BP:
Spring click riveted to the top of the back plate. Approximately 1 3/8 inches long. Used from very early four inch movements through ca. 1895. The F.W. (Ironclad) had it on the alarm barrel until around 1912.
Alarm Click 2: Spring click integral to BP:
Spring clicks integral to the back plate. They are made in the plate stamping process by removing material, then bending the end down so it engages with the projections on the mainspring barrel. Used until around 1899 on the four inch movement.
Alarm Click 3: Traditional click & spring inside BP:
Traditionally shaped click riveted inside the back plate, pressed toward the projections on the barrel by a flat steel clickspring. Commonly seen on clocks with the circular form of the 1885 patent.
Alarm Click 4a: Single-end flat spring click inside BP:
Flat brass spring click whose acting end engages with the projections on the barrel. A rectangular hole in the back plate limits the motion of the acting end. These are commonly found broken.
Alarm Click 4b: Double-end flat spring click inside BP:
Flat brass, double-end spring click whose acting ends engage with the projections on the barrels. The spring click is attached to the back plate at its center. One end is the click for the time barrel, and the other end is the click for the alarm barrel. Two rectangular holes in the back plate limit the motion of the acting ends.
Alarm Click 5: Traditional click & spring outside plate or barrel:
Traditional brass click and clickspring mounted to the outside of the plate or bridge, engaging with a traditional brass ratchet gear.
Alarm Click 6: Traditional click & spring on mainwheel:
Traditional brass click and clickspring mounted to mainwheel, engaging with a traditional brass ratchet gear. The Big Ben has this for the alarm from the beginning.
Alarm Click 7: Projections that engage with openings in mainwheel:
The mainwheel has wedge-shaped openings that engage with projections on a plate attached to the arbor. Used in the last Ironclad movements starting ca. 1924, and probably other later 4 inch movements.
