When installing pipe, flex, data cable or AC/MC in metal studs, there is often a need to make a hole in the stud other than the manufacturer knockout. This tool punches a hole through studs up to 20guage. Once the stud has been punched, you need to use a bushing or insulator to shield the wire or conduit from the rough edges of the steel. Those insulators are the Greenlee 711, 714 and 715 family of items.