A tapping set combines taps and matching drill bits. The point is not the bundle price but consistency: each tap has its tapping drill, which removes the most frequent and most costly mistake.
The reference in the catalogue
The Alpha Coupe set of 7 cobalt 5% taps and 7 Gold&Black drill bits.
See also our hand tools and our Alpha Coupe products.
Tapping drill diameter
It is the mistake that breaks the tap, and it is systematic for anyone who does not know the table by heart. The tapping hole is not drilled at the nominal screw diameter but at that diameter minus the pitch.
For an M8 with a 1.25 pitch, the tapping hole is 6.75 mm, so 6.8 mm in practice. Drilling too small makes the tap work beyond what it can take; drilling too large gives a shallow thread that strips when tightened.
Why cobalt
High speed steel with added cobalt keeps its hardness at higher temperature. On a tap, whose edge works in confined friction in the hole and clears heat poorly, this hot hardness translates directly into tool life, especially on stainless steel and alloy steels.
The technique
A tap is advanced one turn then backed off half a turn, to break the chip. Without this, the chip coils up, packs the hole and jams the tool. And cutting fluid is not optional on stainless steel.
A question before ordering?
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