I recently purchased 2 sets of the pre-ground HSS sets, in 1/4" and 5/16". (catalog/stock# H5870 & 5871) While some of the pre-ground sets may include an internal threading cutting tool, these sets do not.
If anyone is temtped to buy these pre-ground sets, and expecting the internal thread cutting tool, be certain that it's included before purchasing. The internal threading tool is shown and described as included in the H5687 & 5690 sets (costing almost $60 per set).
I don't anticipate that the HSS is a high grade (made in India) but some of the low grade HSS blanks I've gotten from Enco hold up fairly well in any operations I've used them for.