78 



the cut covers half the surface, and leaves the other 

 half to maintain the connection of the crown with the 

 root. Often several cuts are made, one above the other, 



FIGURE 28. 

 Sketch showing tapping systems. 



e. Herringbone. 



f. Two Half Herringbones. 



and along the lower ends of the cut, a groove is made, 

 ending in a drip -tin. 



One advantage of the half spiral is, that the cut runs 

 to one side, and that therefore the tapper does not need 

 to change the position of his knife, hand or arm. If 



