Best Bolts for Pressure-Treated Lumber
Pressure-treated lumber is soaked in copper compounds that eat plain steel — bolts in PT must be hot-dip galvanized or stainless, full stop. Through-bolts beat lags where both sides are reachable, and structural screws now replace lags in code-listed applications. Match the metal to the treatment stamp: ACQ and CA are the corrosive ones.
What to Look For
- HDG (G185) or stainless only — plain zinc fails in ACQ-treated wood.
- Through-bolt critical joints — ledgers, beams, rail posts.
- 1/2-in diameter for ledgers and beams — 3/8 in for lighter brackets.
- Washers both sides — PT crushes under bare heads and nuts.
- Isolate aluminum from PT — flashing and hangers need barriers.
Top Picks
1. Hillman 1/2 x 6 in HDG carriage bolt kits Best overall
Hot-dip galvanized bolts with nuts and washers — the ledger-and-beam standard for ACQ lumber.
Check price on Amazon →2. Simpson Strong-Tie SDWS structural ledger screws Lag replacement
Code-listed structural screws that replace 1/2-in lags with no pre-drilling — ledger boards done right.
Check price on Amazon →3. 316 stainless 1/2-in hex bolt kits For coastal
For docks, seawalls, and salt air — where even HDG eventually surrenders.
Check price on Amazon →What to Avoid
Avoid
- Plain-zinc or bright bolts — copper treatment corrodes them in seasons.
- Aluminum in contact with PT — galvanic corrosion destroys it.
- Undersized 1/4-in hardware on ledgers — connections, not the wood, fail first.
Also in the toolbox
- Ship auger bit set — clean bolt holes through PT without burning
- Cold-galvanizing spray — touch up every cut and scratch on HDG
FAQ
Why do bolts rust in pressure-treated wood?
Modern ACQ and CA treatments are copper-rich preservatives that attack plain steel galvanically — the copper literally plates onto the steel while the steel dissolves. Only heavy HDG (G185) coatings or stainless survive the chemistry.
Through-bolt or lag for a deck ledger?
Through-bolt where you can reach both sides — it clamps instead of threading and cannot pull out. Where access is one-sided, code-listed structural screws (LedgerLok, SDWS) beat traditional lags: no pre-drilling, published load values, higher capacity.
Is stainless necessary, or is galvanized enough?
Hot-dip galvanized (G185) is enough for most inland decks and fences — it lasts decades in ACQ lumber. Go stainless within sight of salt water, for docks and seawalls, or anywhere replacement would mean demolition.
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