What Diameter Stock To Start With Given Thread Choice

[Wreck™Wreck]

However, I am certain that a REAL machinest would have heart failure upon reading this.

Not at all, if making a threaded part that someone else will measure then by all means make it within the stated class fit or particular given dimensions.

If making something for personal use then do it however you want, one may also make non standard threaded parts that will confuse the hell out of someone in the future, 1/4-19, 5/16-15, 3/8-17 and so on.

I am guilty of this little joke.

 

[boostin53]

If making something for personal use then do it however you want, one may also make non standard threaded parts that will confuse the hell out of someone in the future, 1/4-19, 5/16-15, 3/8-17 and so on.

I am guilty of this little joke.

I'm guilty of doing the same thing! I find the looks on people's faces to be funny when they can't find a nut or a bolt that fits my weird choice of thread for a given diameter. I only do it for laughs then eventually tell them.

 

[Wreck™Wreck]

You can find the recommended initial diameters in the machinest handbook if you happen to have one.

This data may be found all over the Web

The Industry nomenclature is:

Major Diameter, this is the nominal bolt size and will include a minimum and maximum.

Minor Diameter, the diameter at the root of the thread, minimum and maximum.

Pitch Diameter, this is the important one, it is roughly halfway between the Major and Minor diameters, also with a minimum and maximum dimension.

Lead, the distance between thread centers, not to be confused with pitch, minimum and maximum values.

Crest and Root, these will either be flat or radiused depending on the thread profile.

Thread Class, the higher the class the closer the dimensions, the lowest thread class is used for common household fasteners, the tightest is used for holding the wings on the airplane.

As seen here, an A thread class designation is external, B is internal.
http://www.engineersedge.com/screw_threads_chart.htm