| 1 | Steerable Pilot Bit | A cutting head with angled faces or a bent housing that allows the drill string to change direction. | Creates and guides the pilot bore along the planned underground alignment. | Soft clay, silt, sand, weathered soil, and mixed near-surface formations. | Commonly about 50–150 mm (2–6 in) pilot diameter, depending on the drill system. | Bit profile, fluid ports, steering response, cutter material, and compatibility with the locating system. |
| 2 | Rock Roller-Cone Bit | A bit using rotating toothed cones to crush and chip hard rock. | Drills pilot holes or advances through competent rock formations. | Limestone, sandstone, shale, cobbles, and other consolidated formations. | Often selected for pilot diameters of approximately 75–300 mm (3–12 in). | Tooth structure, bearing design, rock abrasiveness, required torque, and drilling-fluid circulation. |
| 3 | Downhole Mud Motor | A hydraulic motor powered by drilling fluid to rotate a bit independently of the drill string. | Improves rock penetration and enables controlled drilling in hard or fractured ground. | Hard rock, abrasive rock, cobbles, and formations where surface rotation is less effective. | Common tool diameters range from about 90–200 mm (3.5–8 in), subject to rig capacity. | Flow rate, pressure drop, motor output, bend angle, bit connection, and expected operating temperature. |
| 4 | Backreamer | A cutting or scraping tool pulled through the pilot bore to enlarge and condition the hole. | Prepares the bore for product pipe installation after pilot drilling. | Soil, clay, sand, gravel, and selected mixed-ground conditions. | Typical reaming diameters range from approximately 150–1,200 mm (6–48 in). | Cutter configuration, ground condition, fluid circulation, pullback load, and required bore enlargement. |
| 5 | Hole Opener | A heavy-duty enlargement tool with replaceable cutters for creating a larger, stable bore. | Performs high-volume hole enlargement for large utility, water, sewer, or pipeline crossings. | Hard rock, abrasive formations, cobbles, and large-diameter mixed ground. | Frequently used from about 300 mm to more than 1,500 mm (12–60+ in). | Cutter type, roller protection, centralization, torque requirement, and transport or assembly limits. |
| 6 | Barrel Reamer | A cylindrical reamer that combines cutting surfaces with a barrel-shaped body for bore stabilization. | Enlarges and smooths bores while helping maintain a consistent hole profile. | Clay, cohesive soils, soft rock, and formations requiring controlled cuttings removal. | Commonly available in approximately 200–900 mm (8–36 in) working diameters. | Body length, cutter arrangement, mud-flow capacity, gauge protection, and bore stability requirements. |
| 7 | Drill Pipe | Threaded steel pipe sections that transmit thrust, torque, and drilling fluid between the rig and downhole tool. | Builds the drill string and carries tools through the pilot bore and reaming stages. | Used in virtually all HDD ground conditions with the correct grade and connection. | Individual lengths are often about 3–10 m (10–33 ft); outside diameters vary by rig class. | Tensile capacity, allowable torque, fatigue resistance, connection design, bore radius, and fluid pressure rating. |
| 8 | Drill Stem Sub and Swivel | Connection components that adapt thread sizes, attach tooling, or allow product pipe to rotate independently during pullback. | Connects mismatched tools and reduces torsional stress on the product pipe. | Applicable across soil and rock projects, especially long or high-load installations. | Selected according to drill-pipe connection, product diameter, and pullback load. | Working load, torque rating, pressure rating, thread compatibility, sealing system, and bearing protection. |
| 9 | Drilling-Fluid Jet Nozzle | A replaceable nozzle or port that directs bentonite drilling fluid toward the cutting face. | Cools and lubricates tooling, transports cuttings, and helps stabilize the bore wall. | Most useful in unconsolidated soil, sand, clay, and mixed formations. | Orifice sizes are chosen for the pump, fluid properties, and required flow velocity. | Flow rate, pressure loss, abrasion resistance, plugging risk, nozzle angle, and drilling-fluid formulation. |
| 10 | Product-Pipe Pulling Head | A reinforced attachment that connects the installed pipe or cable bundle to the swivel and drill string. | Transfers pullback force while protecting the product connection during installation. | Used for polyethylene pipe, steel pipe, conduit, cable bundles, and other approved products. | Sized to the product outside diameter, wall thickness, connection method, and pulling force. | Safe working load, pipe grip, load distribution, bend radius, sealing, and compatibility with the swivel. |