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You bought the wrong tap.? Cheap taps are? worthless, as you discovered.

Taps? worth buying :

Balax for thread forming.?

OSG and Emuge for cutting.

I? don't know of another company making? taps that are worth a damn.?? For hand tapping? Use either thread forming taps or Two Flute Gun Taps. For bl;inf holes use Spiral taps? they are usually three flutes

There is? absolutely? no circumstance in which I would bother with a four flute tap. They are weak as hell? - - which you just found out.?

Use a high sulfur? cutting oil? or a specialty? tapping fluid? like TapFree there are many good tapping fluids?

In malleable metals like Steel and Aluminum I prefer to form the threads? instead of cutting.? If you are jobber you need to check the print and see if they are acceptable.

In high hardened steel? I prefer to send it out to an EDM shop but I can tap? pre hard 4140 and 4150? if the hardness is? 48 RC? and not more.

1018 is about the same as A36.? it is a Weee skosh more? machinable? but not worth the money? unless you are running lots of it and need the? better finish.? It takes more skill to get a great finish on A-36.

Cold Rolled is? OK? if you plan on doing little more? than drilling and tapping? but if you plan on machining the mill surfaces then? stay away from the stuff.?? The stresses in the surfaces from the? rolling mil will cause the metal to form banana shapes as you remove stock from one side or the other and you can be chasing your tail trying to get it to lie flat? all day.