Acme Taps?

[Old Iron]

I'm looking for a 5/16 12 LH tap, I'm finding a 5/16 x 12 2/3rds Left Hand ACME Tap. Heres the dumb question what it a 2/3rds tap?

Paul

 

[Tony Wells]

I don't know that I've ever heard that particular reference, but acme taps are typically built to cut in stages, like having a couple of taps stuck end to end. The first section only has to cut partial thread form, since Acme requires such an aggressive removal ratio, it is shared between the two sections. I suppose this case could be a 3 section? I have heard that some actually come as separate taps also.

 

[Old Iron]

Thanks Tony! the one I looked at looked like it was all one tap. And thats the reason I ask.

Paul