The insertion of a coin first lifts a coin plate, then, when pressed, the coin enters the machine lifting the "driving weight". This is connected to a rack and pinion, which ultimately drives the stamp feeding mechanism;
At this stage the coin falls on to the coin guide and rolls past the testing device for ''misformed and abnormal" coins. When the coin has been accepted by the machine, it falls into a chute and thence to a balance arm. This acts as another testing device, as it only operates if the coin is the correct weight. This arm on being fully operated allows the escapement mechanism to rotate and permit the "driving weight", lifted when the coin entered, to draw the feed wheel sufficiently to feed one stamp through to the stamp aperture. Unaccepted coins are rejected and can be picked up in the cup below the stamp aperture.
The roll of stamps is placed on a spindle and held there by a metal arm. The stamps are then fed under a fixed guide bar, over a second guide bar and then under a bar which is pivoted to a lever. When the roll is finished this lever drops causing the "EMPTY" or in later years, "NOT IN USE" plate to drop over the coin hole. The stamps are now fed over a drum containing fixed pins, spaced at a distance of a stamp and fixed into the horizontal perforations, and at every fourth perforation at each side.
The coins used were mainly an old half penny, 1d or a 3d.
The one I have used is the old 1D coin and for that you would get 1D stamp - those was the days of low cost postage!