A 5/16 inch UNC countersunk socket cap screw in stainless steel, 1 inch long. The 5/16 size is a useful step below 3/8, giving you a smaller head and a neater countersink where the 3/8 version would look heavy or leave too little material around the hole in a thin panel. It still carries a respectable clamp load for brackets, cover plates, panel flanges and mounting hardware. The countersunk head sits flush and the internal hex drive lets you reach it in a recess. Stainless steel handles exposure to weather and washdown without staining the surrounding work. Match the countersink angle in your hole to the head so the seat beds evenly.