This Deck Hinge has a flat base, but can be paired with a concave adapter if needed. When mounted, this deck hinge will have a 90 degree angle from its surface, and will require two #10 fasteners upon installation. Although the fasteners and pin are not included, this hinge is designed for 1/4”-20 (6.3-20mm) pin of MH-20, MH-15 or PIN.20. Please note that a bolt cannot be inserted as there is no threading in the hole. Lastly, this deck hinge has a 316 stainless steel mirror finish, being extremely durable for long-term use without corrosion. *fasteners and pin are not included.