The trammel is for work that is beyond the capacity of dividers. Each tram accommedate a 3/16" dia. steel point and are guided along a 1/4" square steel bar 24" long. Above the point on the double tram is a knurled swivel grip that turns freely,making it convenient to swing the tool while scribing or marking circles. The double tram has a 6-32 screw and thumb nut for precise adjustments. Supplied with this trammel is an auxiliary attachment that will accommodate a variety of marking utensils for drawing large circles. The marker attachment is secured in the single tram and will accommodate a standard pencil up to a marker as large as the fine point sharpy. Secured in the attachment picture above (right) is the ultra-fine sharpy.