Two related meanings. In arches and rings, the key is the final brick or bricks driven in at the crown or top to wedge the whole course tight. As a shape, a key brick tapers in width rather than thickness and is used to turn circular linings, as in the key-shaped series used in rotary kilns. Rings are keyed with cut or ground keys, sometimes with steel shims, and a loose key means a loose ring.
Key that ring tight, if you can push the last brick in by hand it's going to spiral in a week.
Also heard as
- key brick
- keystone
- keying
Related terms
Closer
Brick cut to size to fill the last gap in a course, ring or wall.
Arch brick
Tapered brick whose thickness narrows across its width, used to turn thin arches and rings.
Pogo stick
Telescoping prop used to hold bricks against the upper shell of a rotary kiln until the ring is keyed.
Spiraling
Twisting of brick rings out of radial alignment inside a rotary kiln when the lining works loose.