Hanger Bolts and Dowel Screws

What Are Hanger Bolts & Dowel Screws?

Hanger bolts are double-ended fasteners with wood-screw threads on one end and machine-screw threads on the other. They install into wood and provide a machine-thread stud for nuts, washers, brackets, and metal hardware. Dowel screws (double-ended lag screws) have wood-screw threads on both ends and are used to join wood-to-wood with a concealed connection.

What Are They Used For?

• Mounting legs and hardware on furniture, cabinetry, and architectural millwork.
• Suspending pipe straps, electrical/AV fixtures, and sign brackets from wood members.
• Joining wood components end-to-end (dowel screws) without a visible bolt head or nut.
• Wood-to-metal interfaces where the wood side needs a stud and the metal side is secured with a nut/washer.

Benefits of Hanger Bolts & Dowel Screws

• Clean, headless connection: no bolt head showing on finished faces.
• Versatile joining: mix wood, metal hardware, and accessories using the machine-thread end (hanger bolts) or two wood members (dowel screws).
• Field friendly: install with common tools using jam-nuts, driver sockets, or specialty drivers.

Sizes & Threads

Hanger bolts are specified by their machine-thread size × overall length (e.g., 1/4"-20 × 3" or M8-1.25 × 60 mm). Common machine threads are UNC (1/4"-20, 5/16"-18, 3/8"-16) and metric (M6, M8, M10). Dowel screws are specified by diameter × length with wood threads on both ends. Choose a length that provides adequate embedment in the wood member and enough projection for nuts/washers or the mating part.

Materials & Finishes

• 18-8 / 304 Stainless: general outdoor corrosion resistance.
• 316 Stainless: enhanced resistance for coastal/marine or chemical exposure (availability varies by size).
• Zinc-Plated Steel: economical choice for dry interior use.

Installation Basics

1. Layout & pilot holes: Mark centers accurately. Drill a pilot hole in the wood sized near the fastener’s root (minor) diameter; increase slightly in dense hardwoods. For through-mounted parts, drill a clearance hole in the fixture.
2. Driving methods:
   • Hanger bolts: Thread two nuts onto the machine end and jam them together, then drive the wood-thread end into the pilot using a wrench; or use a dedicated hanger-bolt driver socket.
   • Dowel screws: Use a dowel-screw driver, locking pliers with soft jaws, or a clamp-style driver to avoid marring threads. Install into the first piece, then align and drive into the second pilot.
3. Hardware on the machine end (hanger bolts): Secure brackets with flat/lock washers and matching nuts. For frequent removal, consider using a threaded insert or T-nut in the mating part.
4. Do not overtighten: Excess torque can strip wood fibers. If withdrawal resistance is critical, follow engineered guidance for embedment, edge/end distances, and species.

Note: These fasteners are intended for wood. They are not driven directly into concrete or metal; use appropriate anchors, inserts, or nuts as required.

Related Hardware

• Hex nuts, jam nuts, flange nuts, and washers (to match machine thread and material)
• Threaded inserts for wood, T-nuts, and coupling nuts (for extensions)
• Pipe/strap clamps, angle brackets, and hangers that mount to the machine-thread end