Shelf Pin drill guides fit standard shelf pin drilling jigs. As such, their ends are not tapered like other self centering bit guides. Drill bits are easily replaced by simply loosening a set screw, while the spring is replaced by unscrewing the hex drive shank from the knurled body. Shelf pin guides come with standard 1/4" hex shanks for use in Quick Change chucks. Nosepiece is 3/8" dia. Made in the USA.