British Association (BA) Hand Tap Spiral Flute HSS 2BA.

Tapping drill Size 3.9 mm (for information  only)

HAND TAPS (ISO 529)
These are NEW professional quality ground finish straight flute general purpose  tools which can be used for both machine or hand tapping. They are generally  the most economical tool for use on production runs, but are best on materials  that produce chips, or where the swarf breaks readily. Where deep holes are  to be tapped, in materials which produce stringy swarf, other types of taps  may be needed, especially for coarse threads.