Q:
An application with limited space using a #4-40 screw with an assumed tensile strength of 120,000 PSI. This screw continues to break. Do you offer a screw with a higher strength? Also, This screw is used to hold a plate to the end of an air cylinder. It probably jars the fastener on every stroke and has about 6-8 strokes per minute.
A:
Regarding materials, there is a whole range of materials stronger than 120 ksi UTS however it sounds like you not only need strength but also a material that is ductile. I would suggest looking at fasteners made from the age hardened stainless steels such as A286 or 17-4 PH. Known for its high temperature oxidation resistance, A286 bolts also offer excellent high strength capabilities. A286 typically offers a min of 130ksi UTS and 85 yield. 17-4 PH bolting offers varies levels of strength depending on the age hardening process used ranging from 145ksi to 200ksi UTS (H1150 and H900 respectively). Given your application has a repetitive jarring motion you should look at the 17-4 H1150 or the A286 per ASTM A453, 660 A, B or C. These heat treat conditions will give you much more strength but also leave you with a material that is ductile and not brittle which may be a big factor in your fastener application.