3/8 x 4 Stainless Lag Bolt (25-Pack) - Heavy Duty Wood Lag Screw

In this review the 3/8 x 4 Stainless Lag Bolt (25-Pack) is evaluated for contractors, carpenters and DIYers who need corrosion-resistant, heavy duty lag screws for wood and structural repairs. The single biggest reason to buy is the mill certified 18-8 (304) stainless steel construction that resists rust in exterior and exposed projects while meeting commercial ASME B18.2.1 standards. For anyone replacing rusted fasteners or fastening large beams, these lag bolts promise reliable strength and long-term durability.

Key Features

• Diameter and length: The 3/8 in diameter and 4 in length give good shear and pullout strength for medium to large timber connections.
• Material quality: Manufactured from mill certified 18-8 (304) stainless steel for corrosion resistance in outdoor and coastal environments.
• Head design: The heavy duty hex head (9/16 in) provides a positive drive and allows high torque with standard wrenches for secure installation.
• Commercial grade: Packaged and tested to meet ASME B18.2.1 standards, which provides assurance for professional and industrial use.
• Convenience pack: Twenty-five lag screws per bag supply enough fasteners for multiple smaller projects or a single larger job without constant reordering.
• Installation note: A pilot hole is recommended to reduce splitting and to make driving these long stainless lag screws easier and more accurate.

Who It's For

The 3/8 x 4 Stainless Lag Bolt is best for builders, deck contractors, and serious DIYers who need durable, rust-resistant fasteners for structural wood connections, beam attachments, and exterior projects. Its 18-8 stainless construction makes it a practical choice where corrosion is a concern.

Those working on very small trim, light furniture, or where a different head style is required should look elsewhere, and users who require specialty grades higher than 304 stainless (for extreme marine use) may prefer a different alloy. For most residential and light commercial uses, these lag screws are an appropriate and cost-effective choice.

Pros & Cons

Pros

• High corrosion resistance from 18-8 (304) stainless steel for outdoor longevity.
• Commercial/industrial grade testing to ASME B18.2.1 provides consistent sizing and quality.
• Hex head design and 25-pack packaging make installation efficient for professionals and homeowners.
• Customers report strong, durable performance when replacing rusted lag bolts or fastening large beams.

Cons

• 304 stainless is corrosion resistant but not the highest marine-grade alloy, so extreme saltwater exposure may need a higher specification.
• Because these are heavy duty lag screws, a pilot hole is recommended which adds an extra installation step.

Specifications

Diameter	3/8 in
Length	4 in (measured from bottom of head to point)
Head size	9/16 in hex
Material	18-8 (304) stainless steel, mill certified
Quantity	25 lag screws per bag
Standard	Packaged and tested to meet ASME B18.2.1
Installation	Pilot hole recommended

Our Verdict

The 3/8 x 4 Stainless Lag Bolt (25-Pack) is a solid choice for anyone needing dependable, corrosion-resistant lag screws for structural wood work. With mill certified 18-8 stainless steel and ASME testing, it offers good value for contractors and committed DIYers who want long-lasting performance on exterior and load-bearing applications.

Frequently Asked Questions

Are these lag bolts suitable for outdoor use?
Yes. The 18-8 (304) stainless steel construction offers good corrosion resistance for most outdoor and residential applications.

Do I need to predrill holes?
Yes. A pilot hole is recommended to prevent wood splitting and to ease installation for the 4 in length.

How many screws come in a pack?
Each bag contains 25 lag screws, enough for multiple connections or a single large project run.