Hanger Bolts & 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
- 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.
- 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.
- 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.
- 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
Hanger Bolts & Dowel Screws FAQs
See the accordion below for pilot-hole sizing, measuring conventions, installation tools, and material selection.
Disclaimer: This content is general guidance. Always follow product datasheets and applicable codes.
A hanger bolt has wood-screw threads on one end and machine-screw threads on the other for use with nuts/washers. A dowel screw has wood-screw threads on both ends for wood-to-wood joining.
By the machine-thread size and the overall length (e.g., 1/4"-20 × 3"). Dowel screws are measured by diameter and overall length.
As a rule of thumb, drill near the fastener’s root diameter; increase slightly for dense hardwoods. Always confirm with the product guidance for your specific size and wood species.
Use two jam nuts on the machine end or a dedicated hanger-bolt driver socket. For dowel screws, use a dowel-screw driver or soft-jaw pliers to avoid marring.
Pre-drill carefully and avoid edge distances that cause splitting. For frequent assembly/disassembly or higher loads, install threaded inserts or T-nuts instead.
Strength depends on alloy and heat treatment. Choose stainless for corrosion resistance; choose carbon steel where higher strength and interior use are acceptable. Verify working loads with the product data.
Not directly. For metal, pass the machine-thread end through and secure with a nut/washer or into a suitable insert. For concrete/brick, use the correct masonry anchors.
Provide enough embedment in the wood for the load and enough projection for hardware. Follow engineered or manufacturer recommendations for embedment and edge/end distances.
It can. For serviceable joints, use a threaded insert or T-nut in the wood to provide a durable machine-thread interface.
Yes—common machine threads include M6, M8, and M10 for hanger bolts; dowel screws are sized by diameter/length in metric as well.
Flat washers protect surfaces and spread load; lock nuts or thread-locking methods help resist vibration where needed.
Only when the assembly, base material, and hardware are designed for the load and permitted by code. For safety-critical/overhead loads, follow engineered details strictly.