The PMD900A is a 900mm length extension unit which can be added on the floor tom side or the left side of double bass drum setup. Horizonal Pipe Guide Line - Use this center mark on horizontal pipes to line up J30TS clamps. This will ensure that the angle of all toms and cymbals mounted on the horizontal pipe are consistent. Vertical Pipe Guide Line - Curved markings on vertical pipes, every 50mm, allow for easy and precise positioning of horizontal pipes.