Straight flute thread mills come in a large variety of sizes and are crest cutting for internal threads only.
Straight Flute - UN
Stub Acme Internal SPTM Thread Mills
Metric Straight Flute Thread Mills - Solid Carbide - Full Profile
Acme Internal SPTM Thread Mills
Metric 30 degree Helical Flute Thread Mills - Solid Carbide - Full Profile
Metric 15 degree Helical Flute Thread Mills - Solid Carbide - Full Profile