"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. 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.

Harold