Tag: Greenlee Hand Knockout Punch Part Numbers

Dear Mr. Electrician: What are the actual hole saw sizes for the various trade sizes of electrical conduit?  I plan to install a lot of electrical conduit.  I know that I will need to drill with hole saws or use a knockout punch in junction boxes and the circuit breaker panel. Answer: I have posted the hole saw and knockout sizes for electrical conduit below.  For electrician's hole saw kits see here.  When drilling with a hole saw it is important to use a slower spinning drill with a lot of torque rather than a high speed drill.  It is best to drill at 400 revolutions per minute (RPM) or slower when using a hole saw.  Drilling at a slower speed will help the hole saw last longer, and there is less of a danger of the hole saw getting jammed and causing damage or injury.  NOTE: Text links go to applicable products on Amazon.com There is a list of old Greenlee hand knockout punch replacement part numbers at the bottom of this post. I usually use my 1/2" Milwaukee Electric Right Angle Drill when using a hole saw as the torque is very good and the RPM'S are just right.  The extra length of the right angle drill makes it easier to maintain control of the drill if the hole saw does get jammed.  I suggest wearing work gloves when using a right angle drill. When drilling into metal, it is a good idea to oil the hole saw a few times to prevent premature wearing of the hole saw teeth.  I read in a trade magazine of one electrician who puts an oil soaked cut-to-size piece of Felt inside of his hole saws whenever he drills into metal.  As the hole saw heats up from drilling, the oil will trickle down onto the metal being drilled. Put something on the floor to protect it from oil leaks such as flattened boxes or an old piece of plywood.  Although you can probably use most general purpose or motor oils for lubricating when drilling, there are oils made especially for drilling, tapping, and threading.  Amazon sells cutting oil which is used for these purposes.   Electricians Hole Saw Kits on Amazon Two types of hole saw arbors are depicted in the above photo and they are not interchangeable.  The three arbors on the top left can only be used with a hole saw that has the rectangular round shape.  The others screw in to one of two standard size threads. Electrician's Conduit Hole Saw Sizes 1/2″ conduit, drill using a 7/8″ hole saw or 1/2" conduit knockout punch (.885" or 22.5mm). 3/4″ conduit, drill using a 1 1/8″ hole saw or 3/4" conduit knockout punch (1.115" or 28.3mm). 1″ conduit, drill using a 1 3/8″ hole saw or 1" conduit knockout punch (1.362" or 34.6mm). 1 1/4″ conduit, drill using a 1 3/4″ hole saw or 1 1/4" conduit knockout punch (1.701" or 43.2mm). 1 1/2″ conduit, drill using a 2″ hole saw or 1 1/2" conduit knockout punch (1.951" or 49.6mm). 2″...