An ornament consisting of a band or bands of raised short cylinders (roll billet) or square blocks (square billet) placed at intervals. When roll billet alternates with square billet it is called pipeline billet. Radial billet is an uncommon form of billet consisting of a row of half-discs set with their curved faces adjacent to one another. In an arch, the axes of the discs lie along radii of the arch, hence the name.

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