The longer 1 1/4 inch version of the 3/8 UNC stainless countersunk cap screw. That extra quarter inch of reach is the difference between full thread engagement and a screw that only just catches when you are bolting through a thicker panel, a spacer, a bracket stack or a gasket and flange together. The countersunk head pulls flush into a chamfered hole so nothing stands proud of the surface, and the socket drive gives you a positive grip for tightening. Stainless construction keeps it clean in exposed positions. As with any countersunk fastener, make sure the hole chamfer matches the head angle so the load spreads evenly rather than concentrating on a narrow edge.