Size 1/2" x 3/8" Pilot. The Rebore-Zit drill bit is the only drill bit designed to enlarge a previously drilled hole while retaining the existing wire in that hole. The bit is fabricated with a custom made, hollow bodied drill bit containing a free spinning, swivel eyelet mounted to its pilot hole center shaft. Just secure your existing wire onto the eyelet and re-drill your hole to a larger size. The bit will not twist the wire.