Carlisle's HP Purlin Fastener is specifically designed to secure membrane and Pressure-Sensitive (PS) RUSS to structural steel purlins in Carlisle's metal retrofit roofing systems. HP Purlin Fasteners are compatible with 2" (50.8 mm) HP Polymer Seam Plates and 2-3/8" (60.3 mm) Piranha Plates. Minimum penetration is 1-1/2" (38 mm).