Disc
From TrigpointingUK
On man-made structures, such as church roofs, it was sometimes inappropriate to install a rivet into the existing fabric of the building. In such cases, an asphalt disc was poured onto the surface and the rivet installed in that [1].
There are 129 Discs listed in the TP:UK database. One such example is on the turret roof of St Ninian's Church on the Isle of Man.
