As I started looking at antique pocket watches, there was a common term that kept appearing on the description of the timepieces, the movement plate. I started seeing references to full and ¾ plates. I realised that I needed to understand what these terms meant, which is the topic of today’s post.
The main plate is the foundation of a movement. It is traditionally the element around which the remainder of the movement is constructed. The main plate is typically made of brass. Movement plates provide the housing for the inner components of the watch and contain the jewels, pivots, and screw holes. The top plate, which usually contains the manufacturer’s signing name and serial number, can be easily seen by opening the case back and dust cover of an antique watch. The pillar plate is on the other side of the watch and can be seen by removing the dial of the watch. The most common movement plate types are grouped into three basic classifications: Full, 3/4, and Bridge.
The movement plate is a critical part of a watch, without it, the underlying components would be unable to work. Although it is static and has no moving parts, an antique watch would be unable to work without the movement housing. Think of it as the foundations of a building, the construction would soon fall apart without the support of the movement plates.
Full plate movement
The movement of an antique pocket watch contains many components that help to tell the time. The movement plates hold all of these components together. The gear train within full plate in antique pocket watch movements is enclosed between two metal plates while the balance wheel is installed above the top plate. Most early antique pocket watches are almost exclusively full plate designs.
3/4 plate movement
3/4 plates are commonly used when producing smaller, more compact, movement sizes. The balance wheel sits level with the rest of the gear train, rather than on top of the movement plate. The main advantage of the 3/4-plate design compared to that of the full-plate is that the balance wheel is tucked down between the plates of the 3/4-plate movement, making for a thinner watch than the full-plate design, whose balance sits on top of the top plate. The 3/4 plate can be split into two parts. The top plate has about 1/4 cut around the balance, which is flush with the top plate.
Bridge plates are separate pieces that hold the gear train in place and were more commonly used in higher-quality watch movements after 1900. The use of bridge plates allowed more of the gear train to be visible. Occasionally, 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 a ‘finger.’
Hopefully, this brief article helps explain the purpose of the movement plates and the different types available.
Read more about other Movement types and Components.