Knock out punch sizes misleading

[Gregory T]

I bought a set of knockout punches that say they are 1/2, 3/4, etc. the 1/2 is actually 7/8 the 3/4 is actually 1 1/8. I have read and watched videos on drilling holes in your kettle and no one mentions this. As I looked further into it, I’m finding that apparently they are for conduits and the size is not the stated size. Which seems very strange to me. Anyway are there knockout punches that actually make holes the size they say? Or what size punches and from whom are people getting to make a 1/2 and a 13/16 hole? I ended up using a step drill in my old kettle, but I would like to use a punch for my Blichman. The step drill holes aren’t very good

 

[day_trippr]

The same punch is often sold by the conduit size and the actual hole size. If you look for punches by hole size it's not hard to end up with what you want.

fwiw, I used a Greenlee 730BB-13/16 punch for all of the bulkheads in my kettles, but you might take a look at this thread for an alternative...

Cheers!

 

[Gregory T]

Ok so the Greenlee 13/16 is hole size. The 1/2 says it’s 7/8 hole size. I had no idea that it was sold conduit size instead of hole size.

 

[day_trippr]

Ok so the Greenlee 13/16 is hole size. The 1/2 says it’s 7/8 hole size. I had no idea that it was sold conduit size instead of hole size.

Don't feel special, judging from all the similar lamentations over the years you are in a large cohort

Cheers!

 

[Tartan1]

Ok so the Greenlee 13/16 is hole size. The 1/2 says it’s 7/8 hole size. I had no idea that it was sold conduit size instead of hole size.

Greenlee makes both Radio Chassis and Conduit punches. Chassis punches will give you the exact hole size listed on the die eg...1/2" punch = 1/2" hole size. Sounds like you have a set of conduit punches which allows for the outside diameter of an electrical conduit as your example demonstrates, however they will work fine just be mindful you will have to adjust and use a punch size smaller than indicated on the die.

 

[Gregory T]

Couldn’t find a Greenlee 1/2 hole diameter found p/n https://www.mcmaster.com/#34685A27 at McMaster which according to their support is a 1/2 hole diameter.

 

[Tartan1]

https://www.alliedelec.com/product/greenlee/730-1-2/70160546/
https://www.alliedelec.com/m/d/72634815534932ce7faa0f3dff04eee2.pdf

Check out Ebay for used Greenlee punches. Usually listed as "Radio Chassis" #730 followed by the size. I have a quite a few sizes I purchased for my panel build and kettle knockouts. These can be had for a fraction of the cost of new.