“Hand Tap” and “Machine Tap”, are terms that don’t always mean what you might think! These are stale industry “legacy” terms. Originally meant to define a purpose, they can be misleading to people in the industry. They should not define a tap’s modern method of use.
According to some handbooks, the term “Hand-Tap” has traditionally been applied to fractional size taps having a standard general-purpose length. Most manufacturers don’t limit the description to fractional sizes. Assumed to be straight-flute, these are taps whose flutes are provided as a space to accommodate chips created as the tap cuts. Some research suggests the terminology originated in the early 1800’s, when most threading applications were literally done by hand. Yet, when the “Machine Age” hit it’s stride after the 1880’s, the term Hand Tap was still used for taps that were unchanged in design, and now used on machines, as well as by hand.
As “machine” tapping is a much faster operation than turning a tap by hand, chip evacuation became more difficult to control. “Machine taps” would become defined as those with flutes designed with geometry to direct the flow of chips out of the hole. Spiral-point and Spiral-fluted taps fit this category. These alterations in flute geometry improved tap efficiency. Today, with the increasing use of coolant-holes in taps, and external directional coolant-flow, a straight-flute “hand” tap can offer a similar assist with chip evacuation, and yet it is still perceived by some as different than the “machine” tap.
Don’t get hung-up on a name. Both “hand” and “machine” taps sold today are manufactured from the same base materials, and can be used by either method. The decision of which design to use should be influenced by the needs of the job.