دیکشنری تخصصی مهندسی نفت - نسخه آنلاین

n: a master bushing that has four holes symmetrically positioned on its outside perimeter and into which fit four corresponding steel dowels. or pins. on the kelly bushing. When the pins are engaged into the holes and the master bushing turns. the kelly bushing also turns. See kelly bushing, master bushing.