In article , says...

What is the strongest tap (aka one I won't snamp off)

I favor two (or three, for the larger sizes) gun taps
in HSS. These work best for through holes but often can
be used in blind holes with a bit of fiddling.

Purchase ground thread taps in this form from reputable
manufacturers like greenfield, etc and you will be suprised
at how much better they work than hardware store stuff.

If you are having trouble snapping them off, check that:

1) you are drilling with the correct size tap drill. Bigger
is easier.

2) you are using the correct cutting fluid for the job. Do
NOT use a lubricant for this like engine oil, ATF, or any other
lubricating oil. You WILL snap taps if you do that.

3) you are setting the tap up square to the hole.

4) you are backing the tap off after each turn if you
are using four flute taps to break the chips.

Give some specifics about the failures and folks can make
other suggestions.

Jim


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