Metric machine taps
The metric ISO coarse thread is the standard joint in European engineering, and this category is correspondingly the largest in the range: 257 versions to DIN 371 and DIN 376 in HSSE, bright, steam tempered or TiN coated, in form A, form B and form C, from M 1 x 0.25 to M 52 x 5.0.
DIN 371 or DIN 376
Both standards describe the same type of tool and differ in the shank. DIN 371 has a reinforced shank at least as thick as the thread. DIN 376 has a reduced shank that is thinner than the thread and can therefore pass through the finished thread, which matters on deep threads. In the range DIN 371 runs up to M 10 and DIN 376 takes over from M 12. The collet is chosen by the shank, not by the thread size.
Form A, form B or form C
Form A has a long lead of six to eight threads and spreads the cutting load over many teeth. Form B has a spiral point lead of four to five threads and pushes the chips forward out of the hole, which requires a through hole. Form C with a 35° spiral flute lifts the chips back out along the tool, the only way out of a blind hole. Run form B into a blind hole and the chips pack in front of the cutting edge until the tool breaks.
Bright, steam tempered or TiN
Bright is the basic version. Steam tempered tools carry a thin oxide layer that inhibits cold welding and holds lubricant, which helps in soft steels that tend to smear. The TiN layer reaches around 2,600 HV and lowers friction on the flanks. Where more is needed, TiCN or TiAlN are the next step; an overview is in the article coatings for threading tools.
Before cutting
The tap drill decides whether the thread holds: too large and the thread depth is missing, too small and the tool breaks. The formula and the table are in the article calculate tap drill size, lubrication under lubricants.
Sorted by material you will find machine taps among the machine taps with coloured ring, hand tools among the metric hand taps, imperial threads under UNF and among the machine taps. Checking is done with thread plug gauges.
