Greenlee 7308 Knockout Kit Punches and Dies for 2-1/2 Inch, 3 Inch, 3-1/2-Inch, and 4-Inch Conduit, Draw Stud, Sleeve and Case - Hand Tool Knockout Punches - Amazon.com
Greenlee 730-1/2 PUNCH UNIT ASSY, RD .500 (730) - Hand Tool Knockout Punches - Amazon.com
Greenlee 60059 Knockout Punch Unit - Hand Tool Punches - Amazon.com