Ply Gem Perspective is a multi-slide vinyl patio door. The invisible T-lock design is intended for high-performance, high velocity hurricane zones and Missile D impact-resistance ratings. Frame corners are assembled with nearly twice as many fasteners as some competing products with an offset fastening pattern, says the company. Pocket, bypass and bi-parting configurations are available as well as custom sizes up to 10 feet high and 30 feet wide.