Harold sez:

" The only exception is the width of the flat for modified V form
threads, which is not included in most charts, although the minor diameter
is specified."

I didn't do a lot of research on this but, I think the formula I gave is for
the diameter of a bolt for cutting sharp "V" threads on a lathe. Without
going into a lot of "class distinction" I believe the formula will also work
quite well for the basic starting diameter for rods to be threaded (chased
??) with a die. As Harold said, it is OK for us home-shop types. Granted,
it may get into trouble with extremely hard material. Then, one would be
well advised to go to "class".

Bob Swinney




"Harold & Susan Vordos" wrote in message
...

"Robert Swinney" wrote in message
...
for a 1/4 " shaft the major diameter is supposed to be a 1/4 ".
Bill, you have sadi this many times and now I wonder if we both mean
the
same thing by "major diameter".

This is confusing, to say the least. Here is a good approach:

Always take "diameter" to mean the actual outside, full diameter of the
rod
or bolt to be threaded; as in 1/4-20, diameter is 0.250; 3/8-16
diameter
is
0.375, etc. For bolt or rod to thread use the formula:

Bolt size = Diameter - ((1.299 x %) / pitch))

Where diameter is as explained above, % is expressed as a decimal, and
pitch
is the number of threads per inch.

Bob Swinney


I would assume that, for the home shop types, it may be confusing, but
it's
not when a thread is specified. Part of the information provided by
threading charts is the *proper* major diameter, which varies depending on
the nature of a thread. In other words, not all 1/4-20 threads are
created
equally.

One example:

1/4-20 2A
Major diameter range: .2489"/.2408"

1/4-20 3A
Major diameter range: .2500"/.2419"

None of the features of threads are left to discretion. Simply
referencing
the charts will provide the necessary information in order to chase
proper
threads.
Harold