Beck, on Universal Screw. 93 
In addition to these gauges is a cylindrical piece of 
hardened and tempered steel, upon which there is a thread of 
Kg. 2. 
a proper shape and pitch for the screw. It is termed a hob 
(fig. 3) J and by pressing pieces of prepared steel against it 
Eig. 3. 
whilst it is revolving, the screw tools (fig. 4) are made. This 
mode is universally known, and I only allude to it here be- 
