Bolt Types Explained: Hex vs Carriage vs Lag vs Structural

Bolts are the fasteners you reach for when nails and standard screws are not enough — ledger connections, post bases, railing posts, machinery, and anything the inspector will look at twice. The Supply Ontime bolts collection covers all the common families, but picking the right one matters: a carriage bolt where a structural connection is required can fail an inspection, and an uncoated hex bolt in a Los Angeles patio cover will streak rust down the post within a couple of rainy seasons. This guide breaks down the four types you will actually specify on an LA job — hex, carriage, lag, and structural connections — and when each one earns its place.

Quick Answer: Which Bolt for Which Job?

Use hex bolts (with a nut and washer) for general steel-to-steel and wood-to-steel connections where you can access both sides. Use carriage bolts for wood-to-wood connections where you want a smooth, snag-free head — decks, fences, gates, play structures. Use lag screws when you can only access one side of a wood connection — ledgers into rim joists, posts, retaining-wall timbers. For engineered structural connections — post bases, hold-downs, column bases — use the machine bolts or code-listed structural screws the hardware manufacturer specifies.

Hex Bolts: The General-Purpose Workhorse

A hex bolt has a six-sided head driven with a wrench or socket and is designed to clamp two materials together with a matching nut and washer. It is the default choice when both sides of the connection are accessible and you need a strong, removable joint.

Grades Matter

Steel hex bolts are graded by strength. Standard grades handle general work, while Grade 8 bolts — like the yellow-zinc Grade 8 hex cap screws in the store — are among the strongest steel fasteners made and are meant for high-stress bolting. Two rules from the product spec sheets worth repeating: always pair Grade 8 bolts with Grade 8 nuts and washers of the same thread pitch, and if you skip the nut, the bolt must go into a pre-tapped hole with matching female threads.

Where LA Contractors Use Them

Hex bolts show up in equipment mounts, steel connection plates, gate hardware, and bolted hardware like column bases. For anything exposed to coastal air or irrigation spray, choose a zinc or galvanized finish for corrosion resistance.

Carriage Bolts: Clean Heads for Wood Connections

A carriage bolt has a smooth, rounded dome head with no external drive, and a square neck directly under the head. You push it through a pre-drilled hole, and as you tighten the nut on the other side, the square neck bites into the wood and locks the bolt against spinning. That is the whole trick: you can fully tighten it from one side, and the finished face shows only a clean button of steel.

Best Uses

The smooth head is a safety and aesthetics feature — nothing to snag clothing or skin on. That makes carriage bolts the standard for decks, fences, gates, docks, playground equipment, and outdoor furniture. A long galvanized carriage bolt such as the 1/2 in. x 8 in. galvanized carriage bolt will pass through a 4x post and rail assembly with thread to spare, and the hot-galvanized coating stands up to treated lumber and weather — important with pressure-treated wood, which corrodes plain-steel fasteners quickly.

Installation Notes

Drill the hole to the bolt diameter, seat the square neck with a tap of a hammer, and always use a washer under the nut — never under the head. If the bolt spins before the neck seats, back off and re-seat it; a spinning carriage bolt can never be properly torqued.

Lag Screws (Lag Bolts): One-Sided Heavy Fastening

A lag screw — most tradespeople still say lag bolt — has a hex head like a bolt but a thick shaft with coarse wood threads and a pointed tip. No nut: it threads directly into the wood. That makes it the classic choice when only one side of the connection is accessible, such as fastening a ledger to a rim joist, securing post hardware, or pinning landscape timbers in a retaining wall.

Pilot Holes Are Not Optional

Lags develop their strength from thread engagement, and driving one without a pilot hole splits the wood or snaps the shank. The store's 3/8 in. x 3 in. galvanized lag screws call for a 15/64 in. pilot hole and a 9/16 in. drive — typical for the size. Galvanized coatings are the right call for exterior and treated-wood work; browse the full lag screws collection for other lengths and diameters.

Structural Connections: Machine Bolts and Code-Listed Screws

"Structural" is less a bolt shape than a performance class: connections that resist seismic and wind loads and must match what the connector manufacturer and the code require. In seismic Los Angeles this is where precision matters most.

Match the Hardware Spec

Structural hardware tells you exactly what to install. A Simpson Strong-Tie CB44 column base, for example, specifies two 5/8 in. diameter machine bolts, with bolt-hole placement engineered to code-required spacing. Deck tension ties call out a 1/2 in. machine or anchor bolt. Substituting a lag or carriage bolt where a machine bolt is specified voids the connector's load rating — and inspectors in LA check. For the concrete side of these connections, see our guide to wedge, sleeve, and screw anchors.

Structural Screws: The Modern Alternative

Code-listed structural wood screws, such as Simpson Strong-Drive timber screws, are engineered as a high-strength alternative to through-bolting and traditional lags. They are recognized under IAPMO UES ER-192, comply with IRC and IBC framing requirements, and usually need no pre-drilling — a big labor saver on ledgers and multi-ply beams. Many joist and framing connectors are designed around them; our joist hangers buying guide covers which fasteners those connectors accept.

Hex vs Carriage vs Lag vs Structural at a Glance

Choosing Bolts for Los Angeles Conditions

Two local factors should drive your selection. First, seismic loads: any connection that is part of the lateral load path — deck ledgers, post-to-beam, hold-downs — should use the exact fastener the connector manufacturer lists, not a lookalike. Second, corrosion: marine air on the Westside, irrigated landscapes, and the copper-based preservatives in treated lumber all attack plain steel. Galvanized and yellow-zinc finishes are the minimum for exterior work, and every product page in the fasteners collection lists the coating so you can match fastener to environment. When in doubt on a permitted project, match the fastener schedule on your plans — it is cheaper than re-doing the connection after inspection.