Lufkin X46F 6-Inch Red End Extension Wood Rule
Spring joint wood rule with graduated slide that extends up to full 6'. Slide runs under friction in T-slot and has a stop at each end so slide will not fall out. Marked both sides and both edges to 1/16ths of an inch, 16" stud centers in red, regular outside markings. Numbering begins on inside of rule; measurement lies close to the work. To take an inside measurement; open rule to within 6" or less of the distance. Butt square end against one side of opening. Extend slide until it strikes other side. Add measurement on slide to that shown at other end of rule for an exact measure of the opening.