Hex Lag Screw

Lag screws are primarily used for connecting wood-to-wood or wood-to-steel components in structural and construction applications. Common uses include:

• Securing timber framing and beams
• Fastening deck supports and bridge timbers
• Anchoring equipment, light poles, or railings to wood bases
• Reinforcing glulam beams with long, fully threaded “stitch bolts” that prevent lamination separation

Their deep thread design allows them to achieve high withdrawal resistance and strong holding power in heavy timber or dimensional lumber.

While the terms are often used interchangeably, the distinction is important:

• A bolt is designed to be used with a nut, relying on clamping force to hold materials together.
• A lag screw is a self-tapping fastener driven directly into wood without a nut.

Lag screws are rotated by the head, not by tightening a nut. For this reason, they are considered screws, not bolts, even though their heads resemble hex bolts.

Portland Bolt manufactures hex lag screws from ½″ through 1½″ in diameter and in virtually any length.

Stock sizes include:

• Diameters: ½″ – ¾″
• Length: Up to 18″ (imported)
• Grade: ASTM A307 Grade A (mild steel)
• Finish: Plain or hot-dip galvanized
• Origin: Import and domestic

Custom-manufactured lag screws can meet other ASTM, AASHTO, and SAE specifications as required by project drawings.

Lag screws are typically made from low-strength carbon steel under ASTM A307 Grade A but can also be produced in higher strength grades (e.g., A449, A354) or stainless steel when specified.

Finishing options include:

• Plain steel – for general interior use

• Hot-dip galvanized – for corrosion resistance in outdoor or marine environments

• Stainless steel – for architectural or high-moisture conditions

Portland Bolt performs galvanizing in-house, ensuring fast turnaround and consistent coating quality.

Lag screws are available with either hex heads or square heads.

• Hex heads are standard and offer a clean, modern appearance with efficient torque transfer.
• Square heads are used primarily for aesthetic or restoration purposes, providing a rustic or historical look consistent with early construction methods.

Both head styles share the same mechanical strength and installation characteristics.

There are three primary point types used for lag screws:

• Cone point – sharp taper, used in smaller fasteners

• Semi-cone point – standard for Portland Bolt’s lag screws; aids alignment into a pilot hole

• Gimlet point – sharp, self-drilling tip used on small-diameter screws only

Larger-diameter lag screws (½″ and above) use semi-cone points since they require pilot holes for installation. Gimlet points are unnecessary for these sizes and would demand excessive torque.

Pilot holes are pre-drilled openings that allow lag screws to be installed without splitting the wood or breaking the screw head under torque.

For large-diameter lags, the pilot hole diameter should be slightly smaller than the screw’s root diameter to maintain thread engagement while minimizing driving resistance.

Engineers typically determine pilot hole size based on wood species, screw diameter, and load requirements.

The minimum thread length is defined as:

½ of the nominal screw length + ½″, or 6″, whichever is less.

For example, a 10″ lag screw would have:
(10 ÷ 2) + 0.5 = 5½″ of thread.

Longer lag screws or those used for specific engineered applications may require custom thread lengths beyond this standard.

Yes. Portland Bolt can produce custom lag screws with:

• Nonstandard diameters or lengths
• Fully threaded “stitch bolts” for glulam reinforcement
• Custom head markings (company name or logo)
• Nonstandard head dimensions
• Alternative steel grades or finishes

All manufacturing—including cutting, heading, threading, and galvanizing—is performed in-house for complete quality control.

Lag screws are produced through a controlled, multi-step process:

1. Cutting:
   20′ steel round bars are cut to the required length, either sheared or saw-cut for clean, repeatable cuts.
2. Heading:
   The steel end is heated and hot-forged using an upsetter to form the hex or square head. This step also applies head markings.
3. Threading:
   Threads are cut (not rolled) using specialized chasers to form deep lag threads suitable for wood.
4. Pointing:
   A semi-cone point is applied to aid pilot hole insertion.
5. Galvanizing (if required):
   Bolts are hot-dip galvanized in Portland Bolt’s 140,000-square-foot facility for long-term corrosion resistance.

Each stage is performed domestically and in-house, ensuring full control of quality and lead times.

A gimlet point is a sharp, self-drilling tip commonly used on small-diameter lag screws that can be installed without a pilot hole.

However, gimlet points are not recommended for large-diameter screws because the torque required for installation would likely shear the head or split the wood. Portland Bolt uses semi-cone points instead for safety and reliability.

Standard stock includes ½″ to ¾″ diameters up to 18″ or 20″ long, typically imported and supplied with gimlet points.

Lag screws larger than ¾″ in diameter and square-headed lags are rarely stocked in the marketplace but can be custom-manufactured domestically upon request.

When ordering lag screws, always confirm the following:

• Diameter and overall length (measured from under the head)
• Grade and specification (ASTM A307A unless otherwise specified)
• Head type (hex or square)
• Finish (plain, galvanized, or stainless)
• Thread length and point type (standard semi-cone)
• Origin requirement (domestic or import)

Providing these details ensures accurate manufacturing and compliance with your project’s engineering specifications.

Portland Bolt manufactures fully threaded lag screws used for radial reinforcement of glulam beams, often several feet long. These “stitch bolts” prevent separation of laminations over time and are produced to tight thread and dimensional tolerances for long-term performance.