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P.C.D.
From WikiPedalia
Chiefly British variant of B.C.D.. "P.C.D." stands for "Pitch Circle Diameter" but "B.C.D." ("Bolt Circle Diameter") is preferable, because the term "pitch circle" has a different meaning when speaking of sprockets.
(The primary, more correct meaning of "pitch circle " is the circle running through the centers of the chain rollers of a chain engaged with the sprocket.)
