Guidelines for Selecting the Proper Connector

1 Evaluate the Application

Consider the type of structure and how it will be used. These recommendations may not apply to non-structural applications such as fences.

2 Evaluate the Environment

Testing and experience indicate that indoor dry environments are less corrosive than outdoor environments. Determining the type of environment where a connector or fastener will be used is an important factor in selecting the most appropriate material and finish for use on the connectors and fasteners. To help in your decision making, consider the following general exposure information:

Interior Dry Use: Includes wall and ceiling cavities, and raised floor applications of enclosed buildings that have been designed to ensure that condensation and other sources of moisture do not develop.

Exterior - Dry: Includes outdoor installations in low rainfall environments and no regular exposure to moisture.

Exterior - Wet: Includes outdoor installations in higher moisture and rainfall environments.

Higher Exposure Use: Includes exposure to ocean salt air, large bodies of water, fumes, fertilizers, soil, some preservative treated woods, industrial zones, acid rain, and other corrosive elements. Type 316 stainless steel contains slightly more nickel than other grades, plus molybdenum, giving it better corrosion resistance in high-chloride environments.

3 Evaluate and select a suitable pressure-treated wood for the intended application and environment

The treated wood supplier should provide all the information needed regarding the wood being used. This information should include: the specific type of wood treatment used, if ammonia was used in the treatment, and the chemical retention level. If the needed information is not provided then Simpson Strong-Tie would recommend the use of stainless-steel connectors and fasteners. You should also ask the treated-wood supplier for a connector coating or material recommendation.

4 Use the chart below, which was created based on Simpson Strong-Tie testing and experience to select the connector finish or material

If a preservative-treated wood product is not identified on the chart, Simpson Strong-Tie has not evaluated test results regarding such product and therefore cannot make any recommendation other than the use of stainless steel with that product. Manufacturers may independently provide test results or other product use information; Simpson Strong-Tie expresses no opinion regarding any such information.

Simpson Strong-Tie recommendation are as follows:

Low = Use Simpson standard painted and G90 galvanized connectors, or Simpson Strong-Tie® Strong-Drive® screws (SDS) with the double-barrier coating, as a minimum.

Med = Use ZMAX®/HDG galvanized connectors as a minimum. Use HDG fasteners which meet the specifications of ASTM A153, Simpson Strong-Tie® Strong-Drive® SDS screws with double-barrier coating, or Strong-Drive® SD screws with mechanical galvanization, class 55.

High = Use Type 303, 304, 305 or 316 Stainless Steel connectors and fasteners.

Connector Coating Recommendation - Structural Applications

Environment	Untreated Wood	SBX/DOT & Zinc Borate	MCA/MCQ	ACQ-C, ACQ-D (Carbonate), CA-B, CA-C & μCA-C			ACZA	Other or Uncertain
Environment	Untreated Wood	SBX/DOT & Zinc Borate	MCA/MCQ	No Ammonia	With Ammonia	Higher Chemical Content ¹	ACZA	Other or Uncertain
Interior Dry	Low	Low	Low	Low	Med	High	High	High
Exterior - Dry	Low	N/A ²	Med	Med	High	High	High	High
Exterior - Wet	Med	N/A ²	Med ^{3, 4}	Med ^{3, 4}	High	High	High	High
Higher Exposure	High	N/A ²	High	High	High	High	High	High
Uncertain	High	N/A ²	High	High	High	High	High	High

Wood with actual retention levels greater than 0.40 pcf for ACQ, 0.34 for MCQ, 0.21 pcf for CA-B, 0.15 pcf for CA-C and MCA or 0.14 pcf for μCA-C (Ground Contact).
Borate treated woods are not appropriate for outdoor use.
Test results indicate that ZMAX/HDG and the SDS double-barrier coating will perform adequately, subject to regular maintenance and periodic inspection. However, the nationally-recognized test method used, AWPA E12-94, is an accelerated test, so data over an extended period of time is not available. If uncertain, use stainless steel.
Some treated wood may have excess surface chemicals making it potentially more corrosive. If you suspect this or are uncertain, use stainless steel.
Type 316 stainless-steel connectors and fasteners are the minimum recommendation for ocean-salt air and other chloride environments.

5 Compare the treated wood supplier's recommendation with the Simpson Strong-Tie recommendation.

If these recommendations are different, Simpson Strong-Tie recommends that the most conservative recommendation be followed.

Additional information

For additional critical information please see the Preservative Treated Wood Technical Bulletin (PDF), Pressure-Treated Wood Frequently Asked Questions, and General Corrosion Risks.