Screw Dimensions
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: Screw Dimensions
: Screw Dimensions -- lbnoakes	Post Reply	Top of thread	Forum

Posted by: jalmeleh ® 02/18/2008, 11:27:52 Author Profile eMail author Edit

The first number correlates to the diameter and follows the equation: Diameter=(number)*.013"+.060" so a 4-40 screw has a diameter of 4*.013+.060=.112"

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Re: Screw Dimensions
: Screw Dimensions -- lbnoakes	Post Reply	Top of thread	Forum

Posted by: jboggs ® 10/05/2007, 13:07:26 Author Profile eMail author Edit

I have never found any correlation to the numerical screws and any regular fractional units. Its just a standard that has been adopted across the industry, just like numbered and lettered drill sizes.

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Re: Screw Dimensions
: Screw Dimensions -- lbnoakes	Post Reply	Top of thread	Forum

Posted by: CCR5600Design ® 10/05/2007, 12:00:41 Author Profile eMail author Edit

As for the 2,4,6 etc, it has been my understanding those numbers represent the diameter of the screw in 1/64ths of an inch. I do not have a response for the 0 representation. Ron "What we need are more people who specialize in the impossible." - Theodore Roethke

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Re: Re: Screw Dimensions
: Re: Screw Dimensions -- CCR5600Design	Post Reply	Top of thread	Forum

Posted by: Kelly Bramble ® 10/05/2007, 12:45:58 Author Profile eMail author Edit

First number is the size designation, and the second number is the number of threads per inch. see /screw_threads_chart.htm

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Re: Re: Re: Screw Dimensions
: Re: Re: Screw Dimensions -- Kelly Bramble	Post Reply	Top of thread	Forum

Posted by: lbnoakes ® 10/05/2007, 13:16:12 Author Profile eMail author Edit

I don't know if I was just unclear in my original post or if I am misunderstanding you Kelly Bramble but I realized that the first number was related to the diameter of the screw. What I am asking is does some one know specifically how they are related. Like CCR5600Design said he thinks it represents the number of 1/16 of an inch, so a 2-56 would have a diameter of 1/8 (2 x 1/16) and have 56 threads per inch.

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Re: Re: Re: Re: Screw Dimensions
: Re: Re: Re: Screw Dimensions -- lbnoakes	Post Reply	Top of thread	Forum

Posted by: Kelly Bramble ® 10/05/2007, 14:35:22 Author Profile eMail author Edit

Your looking for a relationship between the size and pitch. The one I posted is the only relationship I know. Now there is a .013 increment or multiple between the sizes. The original standard was agreed upon between USA, Canada and UK in about 1948-49. The ideal was to achieve interchangability amoung the three nations. Interchangability makes sense, however I suspect the size increments and pitch developed from experience, manufactucturability and functional reliability. If you look at the picture below, there is a tolerance and size relationship that can be expresses mathematically. The numbers illustrated are at MMC (Maximum Material Condition). My references are Machinery's, #21   Modified by Kelly Bramble at Fri, Oct 05, 2007, 14:36:26

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