5/16-18 x 1 1/2 Square Head Set Screw Cup Point 18-8 (A2) Stainless Steel. A square head screw threaded the entire length. It has a four sided square head at one end and a cup-shaped indentation at the other end. The cup point is the most used style set screw. Designed for fast, permanent and semi-permanent location of parts on shafts with hardness differential of 10-15 Rockwell C points and where cutting in of cup edge on the shaft is acceptable. Stainless Steel 18-8 (A2).