General Tools 523 Adjustable Trammels N/A Made in USA Clamps onto beam 5/8" to 1-1/2" thick of any length. General's adjustable trammels accurately measure and mark distances that are too great for conventional compasses and dividers. For layouts, marking templates, and drawing large circles. 6" off-center eccentric points provide fine adjustment. Points can be replaced with pencils, ballpoint pens, crayons, or soapstone sticks for marking various materials.