Simpson Strong-Tie ZMAX Galvanized Concealed Post Base for 6x6 (CPT66Z)
Simpson Strong-Tie ZMAX Galvanized Concealed Post Base for 6x6 (CPT66Z)
Key Features
Overview
The Simpson Strong-Tie CPT66Z Concealed Post Base is a retrofit post base for nominal 6x6 wood posts. This is a concealed post base designed for anchoring a nominal 6x6 wood post to concrete in deck and outdoor structure applications. Model Number: CPT66Z. If you want a post-to-footing connection that looks cleaner than an exposed bracket while still maintaining the required stand-off above concrete, this is the hardware doing that job.
What matters most here is the design. The CPTZ series uses a knife plate and standoff base arrangement, so the connection is mostly hidden inside the post instead of wrapping around the outside. That gives you a more finished look on deck posts, patio covers, pergolas, and similar wood-to-concrete work. Simpson Strong-Tie also builds in a 1 inch standoff, which is code-required in many permanent exterior applications where posts are exposed to weather, splash, or basement conditions.
Material and finish are a big part of why this bracket makes sense outdoors. The knife plate, washers, and standoff base are made from ZMAX galvanized steel, and the visible standoff base gets an additional flat black textured powder-coat finish for appearance. The supplied 1/2 inch diameter drift dowels are mechanically galvanized. In plain terms, that means the hardware is set up for exterior use and treated lumber conditions where corrosion resistance actually matters.
Installation is straightforward, but it is not a slap-it-together connector. The post gets drilled for the dowels and slotted to accept the knife plate. Simpson Strong-Tie specifically calls out using the knife blade portion as a template to mark hole locations, drilling 1/2 inch diameter holes perpendicular to the post, and cutting a 3/16 inch wide slot in the end of the post. That extra layout work is the tradeoff for the concealed look. On a finished structure, most builders will say it is worth it.
The CPT66Z is also flexible on the concrete side. Anchorage can be cast-in-place or retrofit with adhesive or mechanical anchors, which makes it useful for both new footings and existing concrete work. Simpson Strong-Tie notes installation with 1/2 inch anchor bolts and supplied dowels, and the designer is responsible for specifying anchor bolt type, length, and embedment. That is important because the base itself is only one part of the full connection design.
From a build standpoint, this post base is intended for serious structural outdoor work, not decorative light-duty projects. It is commonly used in deck post connections and other permanent wood structures tied to concrete. One important limitation straight from Simpson Strong-Tie: post bases do not provide enough resistance to prevent rotation at the base, so they are not recommended for non-top-supported installations such as fences or unbraced carports. If your structure is properly braced and top-supported, this is the kind of connector that gives you both a cleaner look and the stand-off protection you want.
See the Full Connector System
This connector is more than a single bracket. The concealed design uses separate parts that work together to anchor the post while keeping the visible hardware to a minimum.
- Includes a knife plate, standoff base, washers, and supplied dowel pins
- Built for nominal 6x6 wood post installation over concrete
Protect the Post End From Moisture
The 1 inch stand-off is not just a measurement on paper. It creates space between the wood post and the concrete so water is less likely to sit at the end grain.
- 1 inch standoff height is code-required in many exposed permanent structure applications
- Helps reduce potential decay at the post or column end
Works in Tight Footing Conditions
When you are laying out posts near footing edges or corners, connection geometry matters. Simpson Strong-Tie provides specific corner and edge layout details for the CPTZ series, which is useful on real deck and porch footings where space is limited.
- Designed for wood-to-concrete retrofit post base applications
- Can be anchored using cast-in-place or retrofit anchorage methods
What's in the Box
- (1) Standoff base
- (1) Knife plate
- (2) Washers
- (3) 1/2 in. diameter dowel pins
Anchor bolts are not included. Simpson Strong-Tie specifies using 1/2 in. anchor bolts, and anchor type, length, and embedment must be specified by the designer.
At a Glance
Key Specifications
| Nominal Post Size | 6 in. x 6 in. |
|---|---|
| Application | Decks, post-to-footings, wood to concrete retrofit |
| Material | Steel |
| Finish | ZMAX galvanized with textured flat black powder-coated standoff base |
| Standoff Height | 1 in. |
| Anchor Bolt Size | 1/2 in. |
| Actual Width | 5.375 in. |
| Weight | 3.66 lbs |
Compatibility
Built For
Pro Tip
Use the CPT66Z knife plate as your drilling template before you slot the post. Simpson Strong-Tie also calls out cutting the 3/16 in. slot roughly 6-1/2 in. up the post if you are using a circular saw, which makes test-fitting the plate a lot easier before final assembly.
Warranty & Support
Tool Nut's Take
Simpson Strong-Tie CPT66Z Concealed Post Base for a Cleaner Structural Finish
If you want a 6x6 post base that does the structural job without putting a bulky bracket on display, this is the one to look at first.
- Who it's for: Builders and serious DIYers installing 6x6 deck or outdoor structure posts on concrete who care about both code-required stand-off and finished appearance.
- Why it stands out: The concealed knife plate design gives you a much cleaner look than typical exposed post bases, and the 1 inch stand-off handles the moisture-management side of the job the way it should.
- Worth knowing: This is not a lazy-day connector. You need to drill the post, cut the slot accurately, and design the anchorage correctly. Also, like other post bases, it is not meant to solve rotation in non-top-supported setups.
Common Questions
- What size post is this made for? The CPT66Z is designed for a nominal 6 in. x 6 in. wood post.
- Can it be used on existing concrete? Yes. Simpson Strong-Tie states the CPTZ anchorage can be cast-in-place or retrofit with adhesive or mechanical anchors.
- Why does it have a 1 inch stand-off? The 1 inch stand-off is code-required for many permanent structures exposed to weather or splash water, and it helps reduce decay at the end of the post.
- Can this post base be used for a free-standing fence or unbraced carport? No. Simpson Strong-Tie states that post bases do not provide adequate resistance to prevent rotation at the base and are not recommended for non-top-supported installations such as fences or unbraced carports.