This may be a simplistic question but then I'm pretty simple...

My thread chart gives the OD of threads, e.g. .250 for 1/4-20 and .312
for 5/16-24.

Is it safe to assume that the OD given is the size of a rod one would
use for that size thread. Is there a rod diameter equivalent to the
75% or 100% tap drill size?

In article , Jim K says...

Is it safe to assume that the OD given is the size of a rod one would
use for that size thread. Is there a rod diameter equivalent to the
75% or 100% tap drill size?

Full thread form for a given thread would be given by the
nominal size, ie 0.250 for a 1/4-20 thread. But like tapping
the amount of force require to drive a die onto a nominal
size piece of stock is really really high. It helps to reduce
the OD a bit to give the die an easier time.

If you can, it also helps to turn a section of the stock down
to nearly the minor thread diamter to help the die to go
on square - if the extra part can be trimmed off later.

Jim

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please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
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Minimum rod diameters for a class 2A (medium class of fit) thread a

1/4-20 .2408
5/16-24 .3042


"Jim K" wrote in message
...
This may be a simplistic question but then I'm pretty simple...

My thread chart gives the OD of threads, e.g. .250 for 1/4-20 and .312
for 5/16-24.

Is it safe to assume that the OD given is the size of a rod one would
use for that size thread. Is there a rod diameter equivalent to the
75% or 100% tap drill size?