Timber Bolts

Timber bolts are most commonly used in wood-to-wood and wood-to-steel connections across industries such as construction, marine, and infrastructure. They are frequently specified in dock and pier construction, timber bridges, boardwalks, and retaining structures. In marine environments, the rounded, low-profile head provides a safer surface than a hex head bolt, reducing the risk of injury or vessel damage in areas of contact. In the Pacific Northwest, these bolts are often referred to as economy bolts due to their cost-saving design that eliminates the need for separate washers.

The defining features of a timber bolt are its oversized, dome-shaped head and the two nubs or fins forged beneath it. These nubs grip into the wood to prevent rotation while tightening the nut on the threaded end, allowing for efficient installation without requiring a wrench on the head. Because the nubs must embed into a wood surface, timber bolts are not used with washers under the head, nor are they suitable for installation directly against steel unless specifically manufactured without nubs. This combination of design elements makes timber bolts both functional and visually unobtrusive in exposed wood applications.

Portland Bolt manufactures timber bolts from ½″ through 1½″ in diameter in most ASTM, AASHTO, and SAE specifications. Commonly produced grades include ASTM A307 Grade A for mild steel applications, though other grades can be provided upon request.

Standard stock timber bolts include:

• Grade: ASTM A307
  

• Diameter: ¾″
  

• Lengths: 8″ to 36″ (in 2″ increments)
  

• Finish: Hot-dip galvanized
  

• Origin: Domestic

Custom orders can be manufactured with nonstandard head sizes, specific thread lengths, or custom head markings such as company logos.

Thread length is determined by bolt size and overall length. The following guidelines apply:

• Bolt lengths ≤ 6″: Thread length = (2 × diameter) + ¼″
  

• Bolt lengths > 6″: Thread length = (2 × diameter) + ½″

Stock thread lengths typically follow this pattern:

• Bolts ≤ 12″: 4″ of thread
  

• Bolts 14″–16″: 6″ of thread
  

• Bolts ≥ 18″: 8″ of thread

For longer or specialized timber bolts, custom thread lengths can be manufactured to meet project-specific requirements.

No. Timber bolts do not require a washer beneath the head. The large, rounded head provides sufficient bearing surface, and the nubs under the head are designed to bite directly into the wood. Using a washer under the head would prevent these nubs from engaging and eliminate their anti-rotation function. In addition to cost savings, this design improves installation efficiency by removing the need for an extra component such as a malleable iron or ogee washer.

The nubs under a timber bolt’s head are integral to its function. They are small raised projections forged into the underside of the head during manufacturing. When installed into wood, the nubs dig in and prevent the bolt head from turning while the nut is tightened from the opposite end. This feature allows a single installer to tighten the assembly without requiring a tool to hold the bolt head in place. Because the nubs rely on wood penetration, timber bolts with standard nubs should not bear directly against steel surfaces.

Standard timber bolts are not recommended for steel-to-steel applications because the forged nubs beneath the head are designed to embed into wood, not metal. However, Portland Bolt can custom-manufacture timber bolts without nubs for use where the bolt head bears on steel. When placing an order, customers should specify that the bolt head is to bear on steel so the manufacturing team can omit the nubs during the hot-forging process. This modification ensures proper seating and torque transfer without damaging the bearing surface.

Timber bolts are typically manufactured from low-carbon steel in compliance with ASTM A307 and supplied with a hot-dip galvanized finish for corrosion protection. Portland Bolt performs all galvanizing in-house, ensuring fast turnaround and consistent coating quality. Custom orders can be supplied in plain finish, zinc-plated, or stainless steel (Type 304 or 316) depending on environmental and design requirements.

Portland Bolt manufactures timber bolts through an in-house hot-forging process that ensures structural strength and dimensional consistency. The process includes:

• Cutting: Steel bar is cut to the required bolt length.
  

• Heading: The end of the bar is heated and forged into a dome head, forming the characteristic rounded profile and embedding the anti-rotation nubs beneath the head.
  

• Threading: Threads are cut or rolled to ASTM specifications.
  

• Finishing: Bolts are hot-dip galvanized for corrosion resistance or left plain as specified.

This vertically integrated manufacturing process ensures dimensional accuracy, consistency, and full domestic traceability.

Timber drive spikes are large, heavy-duty fasteners that resemble nails more than bolts. They are designed to be driven directly into wood rather than tightened with a nut. Unlike timber bolts, drive spikes feature fettered lag threads and do not require the nubs beneath the head, since there is no nut assembly that could cause the head to rotate. Timber drive spikes are ideal for joining wood members where high withdrawal resistance is needed without through-bolting, such as in rail ties, retaining structures, and large wooden beams.

Yes. Portland Bolt can manufacture custom timber bolts to accommodate unique specifications, including:

• Nonstandard head dimensions or profiles
  
• Omission of nubs for steel-bearing applications
  
• Extended or modified thread lengths
  
• Custom head markings or logo embossing

Custom tooling can also be developed to match project-specific designs or historical restoration requirements, ensuring both aesthetic consistency and functional performance.

Timber bolts are particularly well-suited for marine, boardwalk, and pedestrian environments because of their rounded, low-profile head. This design minimizes snag hazards and impact damage, providing a safer, smoother surface if people or vessels come into contact with the fastener. Combined with a hot-dip galvanized coating for corrosion protection, timber bolts provide long-lasting durability and safety in high-traffic or wet environments.