... enough for the casing tube to slide down behind the drill bit assembly.2. When the required depth is reached, rotation ... is reversed carefully, whereupon the reamer swings in , allowing the drill bit assembly to be pulled up through the casing.3 ... Thread: API2 3/8”RegO.D.: 89mmWrench Flats: 65mm3Guide SleeveEffective length: 205mm4DTH-HammerHD55, Cop54, SD5, DHD350R, QL505Casing ShoeL3=90mm L4=63mm ...