Keystones have been used since antiquity at the apex of stone arches to lock the other stones into place. Wedge-shaped blocks, also called Keystones, have also decorated architectural woodwork for centuries. In this capacity they are used not only with curved arches, but also with straight Door or Window Caps (as shown here), as well as with cased openings.
When used with woodwork, the face of the Keystone typically extends slightly above the top of the adjoining mouldings. It "stands proud", meaning its surface is slightly raised relative to the adjacent woodwork.
Most of our Polyurethane Keystones are designed to fit over specific Polyurethane Mouldings. The matching Moulding is listed with each Keystone. (Example: "For MD 1015".) This over-the-moulding feature allows easy adjustment to the overall length of the matching Moulding, as a seam between two Moulding pieces can be hidden behind the Keystone. The use of Keystones can also often avoid additional shipping charges because we can cut the Mouldings in half before shipping.