This is a flat head machine screw with a length of 1 1/2 inches and a diameter of 1/4 inches. The length is the total length of the screw including the head of the screw since the head is intended to be flush with the surface of the material by countersinking the hole into which the screw will be inserted. The thread is UNC (Unified National Coarse) which is for this 1/4 inch screw is 20 TPI (Threads per inch).
