Nylon insert locknuts for use with internal threaded fasteners with 5/16-18 thread diameter. The Nylon collar inserted into the nut resists turning, deforming over screw threads for excellent sealing, locking action. As such, the inner diameter is slightly less than the major diameter. Furthermore, they can retain this tight lock in severe temperature conditions, up to 250n degrees Fahrenheit. Made of 18-8 stainless steel. Strong and corrosion resistant for heavy-duty use. Looking for more steel sign bolts? 95TSS carries them, along with aluminum signs and galvanized steel sign posts.