Lag Screws vs Carriage Bolts?
By The DIYPicks Team · Updated July 2026
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Hillman Zinc-Plated Hex-Head Lag Screws
The workhorse for pulling heavy things tight to studs and joists. Match diameter and length to the load, always drill a pilot hole, and step up to galvanized for anything outdoors.
| Type | Hex-head lag screw (lag bolt) |
|---|---|
| Sizes | 1/4 in., 5/16 in., 3/8 in. dia; 1-1/2 in. to 8 in. long |
| Drive | External hex head (wrench/socket) |
| Material | Zinc-plated steel |
| Best for | Heavy fastening into wood studs & joists |
Everbilt 3/8 in.-16 Zinc-Plated Carriage Bolts
The clean, self-locking way to bolt two pieces of wood together. Perfect where you can reach both sides; pair with a nut and washer and go galvanized outdoors.
| Type | Carriage bolt (round head, square shoulder) |
|---|---|
| Sizes | 3/8 in.-16 thread; 1 in. to 6 in. long |
| Head | Domed round head, no drive (nut-tightened) |
| Material | Zinc-plated steel |
| Best for | Through-bolting wood joints |
Our verdict
Choose by access. A lag screw threads into wood from one side, so it's the pick when you can only reach the front — mounting a bracket, ledger or heavy shelf into a stud or joist. A carriage bolt passes all the way through and is tightened with a nut on the back, giving a stronger, removable clamped joint for playsets, benches, fences and gates where you can reach both sides. Lag screws hold in a single member; carriage bolts clamp two pieces together and self-lock via the square shoulder. Both need a pilot or through-hole, and both should be galvanized or stainless outdoors.