Lufkin® X46N Red End® Wood Rule with 6" Slide Rule Extension, 6' x 5/8"Graduated slide rule extends up to 6". Slide rule runs under friction in t slot. Stops at each end to prevents slide from falling out. Marked both sides and both edges. 6' Red end Extension wood rule, inside read With graduated metal slide rule that extends up to 6" Slide rule runs under friction in t slot at each end to prevent slide from falling out Marked both sides and both edges Graduated to 1 16th of an inch 16" stud centers in red, regular