A heavy duty 6×6 post base for concrete needs three things: a 1 in. standoff that meets code, a corrosion-resistant finish, and the manufacturer’s load table for your exact post and load.
Four screws in the wrong base will fail long before the post does. The hardware at the bottom of a deck or porch post is what holds the whole structure down, and most failures trace back to one of three mistakes: a base with no standoff from the concrete, mild-steel hardware rusting in the weather, or a load number copied from the wrong column of the catalog.
Simpson Strong-Tie makes most of the bases contractors reach for, and its 6×6 lineup splits into standoff bases, wet-set bases, and moment bases for lateral loads. Sorting out which of those you actually need takes about five minutes.
What Separates A Good 6×6 Base From A Cheap One?
Three things decide whether a base holds: standoff height, finish, and fastener count and type. Get those right and the post will outlive the deck boards. Get them wrong and rust, decay, or a pulled-out anchor will find you first.
Simpson’s CBS66 lists a base plate providing a 1 in. standoff clearance required by code, and it also points out that the standoff reduces decay at the post and column ends. That 1 in. gap is the single most important detail. Wood sitting directly on concrete wicks moisture out of the slab and rots from the bottom up. A standoff base lifts the post off the surface so air moves under it.
Finish matters just as much. Simpson finishes the range in Hot-Dip Galvanized, ZMAX, and stainless steel. ZMAX is the standard choice for treated lumber outdoors; stainless steel is what you specify near saltwater or in coastal air. Mild painted steel in either spot is a decision you’ll regret in three or four years.
Which Base Matches Your Pour Schedule?
The base type follows the concrete job. Bases set into wet concrete go in before the pour cures, while retrofit bases bolt onto concrete that’s already hard and finished. Picking the wrong family means either cutting concrete or returning hardware.
It’s a wet-concrete style product and sits in a different family from the standoff bases. The ABW66Z and ABA66RZ adjustable post bases, by contrast, are for 6×6 and rough 6×6 posts and come in ZMAX finish — those get used where the concrete already exists.
Rough-sawn 6×6 is its own problem. Simpson sells separate models for rough 6×6, so a nominal 6×6 base will not fit a rough post correctly. Read the nominal-column-size line on the spec sheet before ordering, because the model number on the box will tell you the truth even if the product photo looks identical.
| Base Model | Best For | Key Spec |
|---|---|---|
| CBSTQ66-SDS2HDG | Quick install, nominal 6×6 | (14) 1/4 x 2 in. SDS screws, HDG |
| CBSQ66SS | Coastal, stainless steel | (14) 1/4 x 2 in. SDS SS fasteners |
| ABW66Z | Retrofit onto existing concrete | (12) 0.148 x 3 in. fasteners, ZMAX |
| ABA66Z | Lighter retrofit, adjustable | (8) 0.162 x 3 1/2 in. fasteners, ZMAX |
| MPBZ | Posts needing lateral resistance | Sleeve design, SDS screws only |
| PB66 | Wet-set, embed in fresh concrete | Embeds after pour, flush surface |
| CBS66 | Standoff on existing slab | 1 in. standoff, 12-ga. base, 10-ga. strap |
Every base in that table uses the manufacturer’s own stainless steel or structural screws for the connection. Off-brand fasteners from a bin won’t reach the load number on the spec sheet. If you’re comparing several bases side by side, a hands-on review of tested 6×6 post base options for concrete can save an hour of catalog reading.
How Do You Read The Load Table Correctly?
You read it by row and column that match your post and your load case — nothing else. The numbers on the Simpson pages shift by finish, fasteners, and configuration, so the exact model number and its row are the only numbers worth trusting.
Simpson lists a CBSTQ66-SDS2HDG allowable-load set of 4,375 / 3,060 / 19,335 for its displayed configuration, and the stainless CBSQ66SS shows 4,375 / 3,060 / 14,420. Those aren’t interchangeable. The ABW66Z table lists 1,190 / 12,935 and the ABA66Z shows 920 / 11,415 — different bases, different columns, different values. Copying the wrong row is how a post gets overloaded on paper while the person reading the table thinks they’re fine.
The wood species group matters too. Load tables separate results by species group, so a Douglas Fir post and a Southern Pine post take different numbers from the same base. Know what you’re building with before reading the table.
What About Moment Bases And Lateral Load?
Simpson’s MPBZ is the one to reach for when the post has to resist sideways force — carport corners, pergola posts, anything taking a lateral load. The catalog says it’s specifically designed to provide moment resistance, and it uses an overlapping sleeve design installed with Strong-Drive SDS Heavy-Duty Connector screws.
One detail matters here. If you substitute lag screws to save a trip to the hardware store, you lose the load rating.
Prices in retail listings change constantly and aren’t set by the manufacturer, so treat any number you see — including a real one like the roughly $205 listing on a 10-pack of PB66 at the time it was captured — as a snapshot, not a quote. Confirm the current price when you order.
FAQs
Does A 6×6 Post Base Need To Sit On A Standoff?
Yes, for most outdoor wood-to-concrete connections. Simpson’s CBS66 lists a base plate providing a 1 in. standoff clearance required by code, and that gap reduces decay at the post end by keeping wood off the slab so air moves underneath.
Can I Use A Nominal 6×6 Base On A Rough-Sawn Post?
Usually no. Simpson sells separate models sized for rough 6×6 posts versus nominal 6×6, and the dimensions do not match. Check the nominal column size line on the spec sheet before ordering, because the two models often look nearly identical in photos.
Why Do Allowable Load Numbers Differ Between Similar Bases?
Finish, fastener type, and configuration all change the rating. Simpson’s CBSTQ66-SDS2HDG shows a 19,335 figure in one displayed configuration while the stainless CBSQ66SS shows 14,420 in its own row. Always read the row that matches your exact model and wood species group.
References & Sources
- Simpson Strong-Tie. “CBSTQ Standoff Column Base.” Source for CBSTQ66-SDS2HDG dimensions, SDS screw count, finishes, and the 4,375 / 3,060 / 19,335 allowable-load set.
- Simpson Strong-Tie. “ABW Adjustable Post Base.” Source for ABW66Z and ABW66RZ dimensions, fastener counts, and the 1,190 / 12,935 allowable-load figures.
- Simpson Strong-Tie. “CBSQ Standoff Column Base.” Source for the CBSQ66SS stainless version, (14) 1/4 x 2 SDS SS fasteners, and the 4,375 / 3,060 / 14,420 allowable-load set.
