Self-drilling/self-tapping fastener

摘要

A self-drilling/self-tapping fastener which is suitable for attaching a sprinkler system to a metal supporting structure has a driving head and an integral shank with a threaded portion. Process-hardening and threading of the shank harden the shank to a degree of hardness that retains sufficient ductility for resisting vibration loads. The drill tip at the end of the shank and the lead threads adjacent the drill tip are locally hardened to a relatively high degree of hardness for drilling and tapping the metal support members. A graduated transition zone separates the high-hardness zone from the lower-hardness zone, which allows for a single fastener to exhibit two distinctly different material properties in one fastener. The fastener through this dual process also exhibits two distinct load-carrying capabilities.