General Tools 520 Precision Adjustable Trammel The General Tools and Instruments 520 Adjustable Trammels draw large circles and measure sizable distances with the accuracy of a divider Fine adjusting screw sets points accurately; points are removable and may be replaced with the pencil holder Die-cast bodies with hardened and grounded steel 3-Inch (76mm) needle-point legs; clamp opening for beam is 3/8-Inch x 3/4-Inch(10 x 19mm) Trammels conform to government specifications GGG-T-661b