Lag Screws vs Carriage Bolts?
By Nate Sawyer, Editor · Updated July 2026
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Hillman Zinc-Plated Hex-Head Lag Screws
Hillman's zinc-plated hex-head lag screws (1/4-3/8 in dia, up to 8 in) are the workhorse for pulling heavy things tight to wood studs and joists, with coarse threads that bite deep and a hex head you torque with a socket. But they almost always need a pilot hole or the wood splits, zinc isn't for outdoor lumber, and a wrench is required.
| 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
Everbilt's 3/8 in-16 zinc carriage bolts are the clean, self-locking way to through-bolt two pieces of wood: the square shoulder sinks in so you tighten the nut with one wrench, and the domed head is tamper-resistant. But it needs a through-hole plus a separate nut and washer, only grips in wood, and the zinc finish rusts 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.
Frequently Asked Questions
- Is a lag bolt the same as a lag screw?
- Yes, they are two names for the same fastener: a hex-head screw with coarse threads that bites into wood from one side. The name varies by region and by retailer, but the part is identical.
- What actually decides between a lag screw and a carriage bolt?
- Access. A lag screw threads into wood from one side, so it is the pick when you can only reach the front. A carriage bolt passes all the way through and is tightened with a nut on the back, which gives a stronger, removable clamped joint but requires you to reach both sides.
- Which should you use to mount a TV bracket or a ledger into studs?
- A lag screw. Its coarse threads bite deep into a single member, and the hex head lets you apply real torque with a socket without cam-out. Carriage bolts only make sense where two pieces are clamped together and you can get a wrench on the back.
- Do you need a pilot hole, and are zinc-plated fasteners OK outdoors?
- A lag screw almost always needs a pilot hole - skip it and you split the wood or snap the screw - and a carriage bolt needs a through-hole plus a nut and washer bought separately. Zinc plating is not for exterior or pressure-treated lumber; use hot-dip galvanized or stainless on playsets, fences, decks and docks.