Pocket Watch Movement Plate Types
Movement plates provide the housing for the inner parts of the watch and contain the jewels, pivots, and screw holes. The top plate, which usually contains the manufacturer signing name and serial number, can be easily seen by removing the back of the watch. The pillar plate can be seen by removing the dial of the watch. Plate types are grouped into three basic classifications: Full, 3/4, and Bridge.
The gear train within full plate pocket watch movements is sandwiched between two metal plates while the balance cock is installed above the top plate. Early American 18s pocket watches are almost exclusively full plate designs.
Identification: The balance cock is attached to the top plate and the gear train is not easily seen.Pictured: A Full-Plate 18s Elign Movement
3/4 Plates were commonly used when manufacturing movement sizes 16s and smaller, offering the ability to produce a watch much thinner when compared to a full plate watch. The balance cock and the top plate were adjacent and flush, requiring a cutout in the top plate of the movement. Many times, the 3/4 plate is split into two parts.
Identification: The top plate has about 1/4 cut around the balance, which is flush with the top plate.Pictured: A 3/4 Plate Example on a 16s Illinois A. Lincoln
Bridge plates are separate peices that hold the gear train in place and were commonly utilized in higher-quality watch movements after 1900. The use of bridge plates allowed more of the gear train to be visible. Some manufacturers created models with "false bridges" to give the appearance of a more expensive and elegant watch. A false bridge has the appearance of being a separate plate but is actually part of the top plate structure. In contrast, a true bridge is a separate plate, usually having the appearance of an "arm" or "fingers."
Identification: The wheels of the gear train are held in place by separate pieces attached to the pillar plate. False bridges have the appearance of being separate bridge plates, and true bridges are actually separate pieces.Pictured: A Bridge Plate Example on a 16s Waltham Crescent St.