On Jan 13, 1:23*pm, "anorton"
wrote:
"Randy333" wrote in message

...

I need to do some thread milling, never did it before!! *I need to cut
2- 1-1/4"-11.5 NPS exteranl threads, a 1-3/4"-16 external and a
1-7/8"-18 internal thread.

I found a thread mill for 11.5 NPS but in the catalog it's listed as
internal only, why? *Any place I can get this at under $300 bucks that
MSC wants?

Remove 333 to reply.
Randy

I have never done anything like this either, but I could see that a tool
meant to cut right-hand internal threads would work better for left-hand
external threads than right-hand external (think about the slope direction
of an external thread versus and internal as you look at it from the
cutter's point of view.)

You would use the same tool to mill either left or right hand
threads. The only thing that changes is the direction of the helix.