This 2-1/2" coarse screw, #2 square drive washer head screw works well with 1-1/2" thick material. The washer head of this screw is the most popular head style because the wide bearing surface of the head does not overdrive at the bottom of the pocket. This is especially important for soft materials such as plywood and composites. The screws are self tapped with a Type 17 auger tip and do not require pre-drilling even the hardest materials. Kreg screws feature a steel shank with a larger diameter than many screws on the market today and provide an impressive and strong screw that wont break easily. For maximum rust resistance see Sun-Seal coated weatherproof screws.