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: Hole saw and knockout punch sizes for electrical conduit are posted below. 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 below go to applicable products on Amazon or Ebay.
There is a list of old Greenlee hand knockout punch replacement part numbers at the bottom of this post. For electrician’s hole saw kits see here.
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.
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″ or 22mm hole saw. 1/2″ conduit knockout punch is 0.885″ or 22.5mm.
3/4″ conduit, drill using a 1 1/8″ or 29mm hole saw. 3/4″ conduit knockout punch is 1.115″ or 28.3mm.
1″ conduit, drill using a 1 3/8″ or 35mm hole saw. 1″ conduit knockout punch is 1.362″ or 34.6mm.
1 1/4″ conduit, drill using a 1 3/4″ or 44mm hole saw. 1 1/4″ conduit knockout punch is 1.701″ or 43.2054mm.
1 1/2″ conduit, drill using a 2″ or 51mm hole saw. 1 1/2″ conduit knockout punch is 1.951″ or 49.6mm.
2″ conduit, drill using a 2 1/2″ or 64mm hole saw. 2″ conduit knockout punch is 2.416″ or 61.3664mm.
2 1/2″ conduit, drill using a 3″ or 76mm hole saw. 2 1/2″ conduit knockout punch is 2.914″ or 74mm.
3″ conduit, drill using a 3 5/8″ or 92mm hole saw. 3″ conduit knockout punch is 3.539″ or 89.9mm.
3 1/2″ conduit, drill using a 4 1/8″ or 104mm hole saw. 3 1/2″ conduit knockout punch is 4.044″ or 102.7mm.
4″ conduit, drill using a 4 5/8″ or 118mm hole saw. 4″ conduit knockout punch is 4.544″ or 115.4176mm.
5″ conduit, use a 5 1/2″ or 140mm hole saw.
6″ conduit, use a 6 5/8″ or 168mm hole saw.
|Electrical Conduit Trade Size||Hole Saw Size|
For Conduit or Fitting
|Drill or Hole Saw Size For |
NPT Tapered Threaded Tap.
Taper is 3/4"per foot.
|Tap Thread Size|
|1/8" Pipe or Fixture Nipple (NPS)||13/32"||Q (21/64" or 0.332"), (NPS 0.348" S)||27 Threads Per inch|
|1/4" Pipe or Fixture Nipple (NPS)||35/64"||7/16" (NPS 29/64")||18 Threads Per Inch|
|3/8" Pipe or Fixture Nipple (NPS)||43/64"||9/16" (NPS 19/32")||18 Threads Per Inch|
|1/2" or 16mm Conduit (NPS)||7/8" or 22mm||45/64" (NPS 47/64")||14 Threads Per Inch|
|3/4" or 21mm Conduit (NPS)||1 1/8" or 28mm||59/64" or 7/8" (NPS 15/16")||14 Threads Per Inch|
|1" or 27mm Conduit (NPS)||1 3/8" or 35mm||1 5/32" (NPS 1-3/16")||11.5 Threads Per Inch|
|1 1/4" or 35mm Conduit||1 3/4"or 44mm||1 1/2"||11.5 Threads Per Inch|
|1 1/2" or 41mm Conduit||2" or 51mm||1 47/64"||11.5 Threads Per Inch|
|2" or 53mm Conduit||2 1/2" or 64mm||2 7/32"||11.5 Threads per Inch|
|2 1/2" or 63mm Conduit||3" or 76mm||2 5/8"||8 Threads per Inch|
|3" or 78mm Conduit||3 5/8" or 92mm||3 1/4"||8 Threads per Inch|
|3 1/2" or 91mm Conduit||4 1/8" or 104mm||3 3/4"||8 Threads per Inch|
|4" or 103mm Conduit||4 5/8" or 118mm||4 1/4"||8 Threads per Inch|
|5" or 129mm Conduit||5 1/2" or 140mm||5 9/32"||8 Threads per Inch|
|6" or 155mm Conduit||6 5/8" or 168mm||6 11/32"||8 Threads per Inch|
As an alternative to hole saws, knockout punches can be used. You would drill a pilot hole sized for the draw stud of the punch using a step drill or a small hole saw. Then use a hand knockout punch or a hydraulic knockout punch to make the desired size hole.
KNOCKOUT PUNCH OPERATING INSTRUCTIONS
I found an old set of knockout punch instructions with a parts list among my father’s tools. I scanned it and broke it up into sections for easier viewing. The paper is not in the best condition as I surmise that it is from the early 1960’s.
Below are the operating instructions for Greenlee electricians hand knockout punches.
GREENLEE HAND KNOCKOUT PUNCH REPLACEMENT PART NUMBERS
The following two images depict the replacement part numbers for Greenlee hand knockout punches. I do not know how useful they will be today for obtaining replacement parts for Greenlee knockout punches.
In addition the hole size of each knockout punch is provided.
Listed above are dimensions of the knockout punch parts, and their Greenlee part numbers.
Depicted above are dimensions of the knockout punch parts, and their Greenlee part numbers.
The front and rear pages of the Greenlee Knockout Punch Operating Instructions and Parts List is below.
See my post describing various electrical conduit types.