# 5-40 Machine Screw not so popular?



## AssassinXCV (Aug 4, 2012)

While designing an engine in Autodesk Inventor, I looked through the machine screws that they had models for.

Looking for screw sizes, a 1/4" screw would be too large, so I opted for a 1/8" screw which is a #5-40. Going to hardware stores I see they have #8, #6, and #4, completely skipping over #5. Why aren't #5 machine screws used as much? They seem like they'd be the standard over #4 or #6 due to it being an EXACT outer dimension of 1/8".

The diam of a #4 screw is about 0.112", and #6 screw is 0.1380". What makes these odd sizes BETTER than an exact 0.125" screw?

Able to pick up some online at http://www.microfasteners.com/catalog/products/SSCSCA.cfm or http://www.fastener-express.com/socket-head-cap-screws-alloy-steel.aspx, way better prices than Fastenal

Ian


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## Brian Rupnow (Aug 4, 2012)

I'm not sure why they are not more popular. I know that I have built many engines and I pretty well have standardized on #5-40 shcs and #10-24 shcs. I buy mine through Brafasco or Fastenal here in Ontario, Canada. ---Brian


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## rhitee93 (Aug 4, 2012)

I would assume it is for the same reason none of the odd numbered sized are very popular, but i don't know why that is.


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## kvom (Aug 4, 2012)

I tend to use 5-40, 8-32, and 10-32 screws for almost everything smaller than 1/4.  I order mostly from Enco.


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## cfellows (Aug 5, 2012)

I agree, 5-40 screws seem like the logical choice over 4-40 and/or 6-32.  The other question, why is 2-56 favored over 3-48?  A 3-48 screw is about .093" or 3-32".  Seems like a more logical choice.  I use all sizes from 0-80 on up.  The size I use is often determined by the head diameter.

Chuck


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## nemoc (Aug 5, 2012)

I use 5-40 a lot and have a good supply of screws from 2-56 to 10-32.  Because  
local prices are high and variety is low I order almost everything from http://www.mcmaster.com/   They have a huge stock and ship fast.

Craig


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## IronHorse (Aug 5, 2012)

I agree that 5-40 is near imposible to find in the local hardware stores, but the nice thing about them is that you can directly tread a 0.125 rod.


IronHorse


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