The majority of flushometers supplied by Sloan since 1964 feature the H-551-A adjustable tailpiece. The valve tailpiece connects to the control stop with a sliding O-ring seal. The H-551-A adjustable tailpiece standard length is 2-1/16 in (54 mm). This is designed for a standard flushometer installation in which the distance between the centerline of the valve and the centerline of the water supply inlet is 4-3/4 in (121 mm). The adjustable tailpiece allows for a variance of +/-1/2 in (13 mm) from this nominal dimension.