Screw Chek’r guide q
- Thread starter Muh Muh
- Start date
Welcome from farm country south of Chatham.
Short answer to your question - I have no idea. If you find out elsewhere, please come back and post here.
It isn't mentioned in the instructions for the screwchecker. My screw checker has the same hole as yours but that hole has no associated threads so it can't really be called a screw of any size let alone a number 7 (which I "think" is only a wood screw size). Mine actually measures 0.168 not 5/32. Mine has a similar 9/32 hole that is also actually a bit bigger than labelled.
There is no mention that I could find of a number 7 screw in machinery's handbook nor in any of my references. That no proof of its existence or lack there of, but it's a good indication that it's pretty rare.
Maybe it's to help identify tweeners..... LOL!
Short answer to your question - I have no idea. If you find out elsewhere, please come back and post here.
It isn't mentioned in the instructions for the screwchecker. My screw checker has the same hole as yours but that hole has no associated threads so it can't really be called a screw of any size let alone a number 7 (which I "think" is only a wood screw size). Mine actually measures 0.168 not 5/32. Mine has a similar 9/32 hole that is also actually a bit bigger than labelled.
There is no mention that I could find of a number 7 screw in machinery's handbook nor in any of my references. That no proof of its existence or lack there of, but it's a good indication that it's pretty rare.
Maybe it's to help identify tweeners..... LOL!
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First of all welcome from the Cowichan valley on Vamcouver island.
After reading your post I went out to my shop and got out my Screw Chek'r. It also has the extra hole on the left side. On mine down the left side are the fractional sizes that match up with machine screw numbers. 5/32 is between a number 6 and number 8 and you will notice the number 23 under the extra hole beside the number 5/32. That hole is the clearance hole size for 5/32. As far as I know there is no #7 machine screw size. I hope this clarifies this a little.
I also have a Machinist Calc Pro calculator. I tried entering a number 7 thread size and I just came back with an error message
After reading your post I went out to my shop and got out my Screw Chek'r. It also has the extra hole on the left side. On mine down the left side are the fractional sizes that match up with machine screw numbers. 5/32 is between a number 6 and number 8 and you will notice the number 23 under the extra hole beside the number 5/32. That hole is the clearance hole size for 5/32. As far as I know there is no #7 machine screw size. I hope this clarifies this a little.
I also have a Machinist Calc Pro calculator. I tried entering a number 7 thread size and I just came back with an error message
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Hmmmm. Dunno how I missed that. I'll have to look again.
Anyway, that lists the same thread pitches as a #8 so I think that solves the mystery.
A #7 screw would fit the #8 threaded holes to identify the pitch but a #8 would not fit the 5/32 hole.
Well done @whydontu !
The only remaining question is why call it 5/32 instead of #7?
Maybe 5/32"-32 BSW?
Works too.
Darn - I was just in the barn making a balance ring and forgot to check pg 1232 of machinerys handbook.....
gerritv
Gerrit
BSW is 55 degrees, hard to spot without an optical comparator or the like.
@Muh Muh - I got to the shop after the grandkids left. My working copy of the Machinery's Handbock is the 29th edition 2012. I also have an older version "someplace" - prolly in a cardboard box that hasn't been unpacked yet from when we moved to the farm.
Pg 1232 in my edition is about grinding wheel recommendations for hardened tool steel! LOL!
The section on Machine Screws doesn't start till pg1643.
I was not able to find the latest version of the info WhyDon'tYou posted. I thumbed through all the pages again and still couldn't find any mention of a #7 screw. Every chart in the book skips from 6 to 8 with no 7.
So much for new books!
I'm sticking to the conclusion reached with @whydontu's help.
His chart lists the same thread pitches for a #7 as for a #8. A #7 screw would fit the #8 threaded holes to identify the pitch but a #8 would not fit the 5/32 hole. So the holes can be used to correctly identify both a #7 and a #8 screw.
I still wonder why the hole is labelled 5/32 instead of #7 though.