Lag Bolts vs Wood Screws
Lag bolts and wood screws both fasten wood, but they are built for very different loads. Using a wood screw where a lag bolt is needed is one of the most common causes of a failed deck or beam. This guide compares the two and shows when to use each.
What Is a Lag Bolt?
A lag bolt, also called a lag screw, is a heavy-duty fastener with a coarse thread and a hex head. It is driven with a wrench and is used for high-load wood connections such as decks, beams, and heavy framing. It has a sharp point and cuts its own thread into wood.
What Is a Wood Screw?
A wood screw is a lighter fastener with a tapered body and a sharp point. It is driven with a screwdriver or bit and is used for general carpentry, furniture and light framing. It holds well in wood but is not designed for structural loads.
Lag Bolt vs Wood Screw: Key Differences
| Feature | Lag Bolt | Wood Screw |
|---|---|---|
| Head | Hex, driven with a wrench | Flat, pan or round, driven with a bit |
| Thread | Coarse and deep | Fine to medium |
| Load capacity | High | Light to medium |
| Typical use | Decks, beams, heavy framing | Furniture, cabinetry, general carpentry |
When to Use a Lag Bolt
Choose a lag bolt when the connection carries structural load, when you need high pull-out strength, or when the fastener will be tightened with a wrench. Pre-drill a pilot hole to prevent splitting, especially in hardwood.
When to Use a Wood Screw
Choose a wood screw for lighter work where speed and a flush finish matter. Wood screws are not a substitute for lag bolts in structural joints.
FAQ
Can I use a wood screw instead of a lag bolt?
Only for light loads. For structural connections such as deck ledgers or beams, use a lag bolt or an engineered structural screw.
Do lag bolts need pilot holes?
Yes, especially in hardwood. A pilot hole prevents splitting and makes installation easier.
Bolts for Heavy Connections
SolidLink supplies lag bolts and other fasteners in galvanized and stainless steel. Browse our bolts or fasteners category, or contact us for a quote.
