The socket head cap screws are 100% Stainless Steel 18-8 (304) which offers a high level of chemical and corrosion resistance. Thread Diameter: 4# Inch; Total Length: 1-1/4 inch (Head Included); Thread Count:40 Package Included:50 x Flat Head Socket Cap Screws Flat Head Socket Screws are great to have around for use in wood and wet environments. With a low-profile, countersunk head, flat socket head cap screws are ideal for applications requiring a strong fastener with a flush mount. For example, flat socket cap screws are often used in projects what require moving parts to pass over a fastened area. Allen (hex socket) drive is a six-sided recess for use with an allen wrench (hex key).