High Quality Heavy Duty Hex Head Lag Bolt Wood Screws Zinc Plated Carbon Steel Coarse Threads Sizes M6-M20

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What is a Lag Bolt?

A Lag Bolt (also known as a Lag Screw) is a large, heavy-duty fastener used to join heavy timber or other materials that require a strong connection. Unlike a standard machine bolt, which requires a nut to secure it, a lag bolt is self-tapping and is driven directly into wood or other materials.

It features a hexagonal or square head designed to be driven with a wrench or socket (not a screwdriver), and a coarse, deep thread that provides excellent holding power. Because of its size and thread design, a pilot hole must typically be pre-drilled to prevent the wood from splitting.

Material

Lag bolts are manufactured from various materials depending on the strength and environmental requirements:

Surface Treatment

Surface treatments protect the bolt from corrosion and can also enhance appearance.

Specifications & Sizes

Lag bolts are available in both Imperial (inch) and Metric (millimeter) sizes.

Common Sizes

Key Parameters

• Thread Type: Coarse, sharp threads designed for wood.

• Standards:

  • USA: ASME B18.2.1

  • Metric: DIN 571 (Hexagon Head Wood Screws)

• Strength Grades:

  • SAE J429 Grade 2 (Low carbon steel)

  • SAE J429 Grade 5 (Medium carbon steel, heat-treated)

  • SAE J429 Grade 8 (Medium carbon alloy steel, heat-treated)

Application Areas

Lag bolts are essential in construction and heavy assembly where standard screws are insufficient.

1. Timber Framing & Construction: Securing large wooden beams, posts, and rafters.

2. Decking & Fencing: Attaching ledger boards, fence rails, and heavy brackets.

3. Furniture Manufacturing: Assembling heavy wooden furniture, workbenches, and shelving units.

4. Mounting Hardware: Securing heavy equipment, brackets, and machinery to wooden floors or walls.

5. Automotive & Trailers: Attaching wooden bed liners to truck frames or wooden decks to utility trailers.

6. Marine & Docks: Building docks, piers, and other saltwater-exposed wooden structures (using stainless steel or bronze).

7. Playgrounds & Outdoor Structures: Building pergolas, gazebos, and swing sets.

Excellent Case Example

Project: Building a Heavy-Duty Wooden Deck

Situation:
A contractor is building a large residential deck. The main support structure involves attaching a double 2×12″ laminated ledger board to the side of a house. This ledger board will support the entire weight of the deck, so the connection must be extremely strong and secure.

Why Lag Bolts are the Right Choice:

• Strength: Standard wood screws would not provide enough shear strength to hold the deck safely.

• No Access for Nuts: Unlike a through-bolt (machine bolt), a lag bolt can be installed from the outside without needing access to the interior side of the house’s rim joist.

• Holding Power: The coarse, deep threads of the lag bolt bite deep into the solid wood of the house’s rim joist, creating a powerful clamping force.

The Solution:
The contractor uses 5/8″ x 5″ Hot-Dipped Galvanized Hex Lag Bolts.

1. Pilot Holes: They pre-drill clearance holes through the ledger board and pilot holes (slightly smaller than the bolt’s shank) into the house’s rim joist to prevent wood splitting.

2. Installation: Using a high-torque drill with a socket attachment, they drive the lag bolts through the ledger board and deep into the rim joist.

3. Spacing: They place the lag bolts in a staggered pattern at 16-inch intervals along the ledger board, ensuring the load is evenly distributed.

Result:
The deck is securely fastened to the house. The hot-dipped galvanized coating ensures the bolts will resist rust for decades, even in rain and snow. The large hex head and coarse thread provide a connection strong enough to meet building codes and ensure the safety of the family using the deck.