Used to promote air circulation and help prevent water and debris from collecting behind deck ledgers, these fiberglass-reinforced polypropylene spacers are 5/8 inch thick and 2 1/2 inches in diameter, and have an 11/16-inch–diameter hole for a bolt or lag. Test results of connections made with the spacers are available at the company’s website. About $25.50 per dozen. deck2wallspacer.com