Sealtite Kwikseal ZXL Woodbinder screws are self-drilling screws designed to attach metal roofing & siding to wood purlins on post-frame & residential metal roof applications. Stitch screws are designed specifically to fasten overlapping panel together. Coated screws feature a tough 2.5 mils of powder coating that will not chalk or fade due to the UV inhibitor in all colored coatings. 5/16" cupped HWH with a molded ZAMAC 5 Zinc-Aluminum alloy provides lifetime protection against red rust on the head & washer. The ZAMAC 5 alloy provides more strength than more common ZAMAC 3 alloy. You may obtain a free copy of the written warranty upon request. Washer face design helps to capture rubber EPDM washer even when driven at an angle. Threads transition from fine to coarse to generate superior holding strength in various wood substrates. Sharp point with pronounced lead thread consistently drills high-tensile 29 & 26 gauge steel with no “point walking".