A thread tap includes a shaft and teeth. The shaft includes helical passages from the threading end to the base end of the shaft. Each passage opens through an aperture in the threading end. A second tap includes a cap and the shaft includes an axially extending passage. The cap is coupled to the threading end and at least partially defines apertures in fluid communication with the passage and the exterior of the tap. A third tap includes teeth spaced apart by a plurality of linear flutes. The shaft includes a central passage and a plurality of flute passages. Each flute passage extends radially outward from a common location in the central passage to a corresponding one of the flutes. The central passage is closed to a terminal end of the threading end.

A thread tap includes a shaft and teeth. The shaft includes helical passages from the threading end to the base end of the shaft. Each passage opens through an aperture in the threading end. A second tap includes a cap and the shaft includes an axially extending passage. The cap is coupled to the threading end and at least partially defines apertures in fluid communication with the passage and the exterior of the tap. A third tap includes teeth spaced apart by a plurality of linear flutes. The shaft includes a central passage and a plurality of flute passages. Each flute passage extends radially outward from a common location in the central passage to a corresponding one of the flutes. The central passage is closed to a terminal end of the threading end.

A pipe-tapered-thread machining spiral tap includes a tapered thread portion that is circumferentially divided by flutes into a plurality of lands. Each of at least one of the lands has a cutting edge that extends along a corresponding one of the flutes. The flutes are made of a plurality of spiral flutes that are three, four or five spiral flutes each having a helix angle that is not smaller than 30 and smaller than 50. A flute width ratio AG/(AG+AL) is 0.3-0.5, where AG represents a central angle which is subtended by each of the flutes and which is defined at a center corresponding to the rotation axis in a cross section that is perpendicular to the rotation axis, and AL represents a central angle which is subtended by each of the lands and which is defined at the center in the cross section.

A pipe-tapered-thread machining spiral tap includes a tapered thread portion that is circumferentially divided by flutes into a plurality of lands. Each of at least one of the lands has a cutting edge that extends along a corresponding one of the flutes. The flutes are made of a plurality of spiral flutes that are three, four or five spiral flutes each having a helix angle that is not smaller than 30 and smaller than 50. A flute width ratio AG/(AG+AL) is 0.3-0.5, where AG represents a central angle which is subtended by each of the flutes and which is defined at a center corresponding to the rotation axis in a cross section that is perpendicular to the rotation axis, and AL represents a central angle which is subtended by each of the lands and which is defined at the center in the cross section.

A thread forming tool for forming an internal thread in a workpiece includes a shank and a thread forming portion, which are rotatable around a common longitudinal axis. The thread forming portion includes a plurality of radially protruding lobe portions that are circumferentially spaced-apart by relief portions. The lobe portions have, in the longitudinal direction, a plurality of thread forming profiles and in the longitudinal direction a plurality of thread grooves. Each thread forming profile includes a radially outermost ridge connected to a first flank and a second flank, wherein a first flank of a first thread forming profile is connected to a second flank of an adjacent second thread forming profile via a thread groove. The flanks of at least one first thread groove enclose a first angle, which is smaller than a second angle enclosed by the flanks of at least one second thread groove.

A thread forming tool for forming an internal thread in a workpiece includes a shank and a thread forming portion, which are rotatable around a common longitudinal axis. The thread forming portion includes a plurality of radially protruding lobe portions that are circumferentially spaced-apart by relief portions. The lobe portions have, in the longitudinal direction, a plurality of thread forming profiles and in the longitudinal direction a plurality of thread grooves. Each thread forming profile includes a radially outermost ridge connected to a first flank and a second flank, wherein a first flank of a first thread forming profile is connected to a second flank of an adjacent second thread forming profile via a thread groove. The flanks of at least one first thread groove enclose a first angle, which is smaller than a second angle enclosed by the flanks of at least one second thread groove.

A sintered material includes a first material and a second material, the first material being partially stabilized ZrO.sub.2 having a crystal grain boundary or crystal grain in which 5 to 90 volume % of Al.sub.2O.sub.3 is dispersed with respect to a whole of the first material, the second material including at least one of SiAlON, silicon nitride and titanium nitride, the sintered material including 1 to 50 volume % of the first material.

A sintered material includes a first material and a second material, the first material being partially stabilized ZrO.sub.2 having a crystal grain boundary or crystal grain in which 5 to 90 volume % of Al.sub.2O.sub.3 is dispersed with respect to a whole of the first material, the second material including at least one of SiAlON, silicon nitride and titanium nitride, the sintered material including 1 to 50 volume % of the first material.

A tool shank holder includes a body comprising a shank-receiving end and a bit-receiving end. The shank-receiving end is configured to operably receive a shank of a tool and the bit-receiving end is configured to operably receive a driver bit. A connector is provided at the shank-receiving end that is configured to directly connect the shank-receiving end to the shank of the tool.

A tool shank holder includes a body comprising a shank-receiving end and a bit-receiving end. The shank-receiving end is configured to operably receive a shank of a tool and the bit-receiving end is configured to operably receive a driver bit. A connector is provided at the shank-receiving end that is configured to directly connect the shank-receiving end to the shank of the tool.