Capsquares
Capsquares a, belong to the fittings of the gun carriage and are used to secure the trunnions of the gun barrel firmly in the lower bearings of the trunnion holes. They are attached to the outsides of the carriage cheeks by a small chain, and a protruding part, the beard, engages the mortise at the front of the lower bearing.
Source: Rumpf, H. F.: Allgemeine Real-Encyclopädie der gesammten Kriegskunst (Berl. 1827)