Features & Benefits: All cones are self-centering for accuracy; 2 cones for holes up to 40mm; 4 reverse cones for bolts and nuts up to 19mm; Machined aluminum for durability; Pointers fit all tram gauges; These universal self centering cones will make all measuring more accurate. No more guessing whether you are in the center of the hole or bolt. They attach to 3/8" pointers that will fit in all tram gauges.