[ mg J 
. bow, it will cut-exaétly a ferew, the threads of which will be- 
at the fame diftance as thofe of the wire on the fteel; be- 
caufe the wire ferves as an outfide fcrew and the lead as a 
{crew at the infide; fo that whatéver motion the vice receives ° 
from ‘this caufe in the revolutions of the fteel is communicated 
by the bar (ee) to the knife, the edge of which cuts the 
threads on the polifhed end of the fteel which is intended for” 
the original tap. - 
Ir’ double threads, &c. aré réquiréd, there muft be an ad~* 
juftment’ by which the knife may be moved the thicknefs of 
each additional thread, which may be eafily’ effected by collets 
or by an adjufting ferew. The wire is then to be lapped on™ 
the cylindrical fteel, in a double or triple, &c. inftead of a 
fingle thread, taking care that it-fhall be difpofed evenly. and - 
well faftened.- 
