CITY WATER SYSTEMS 493 



from the top of the hydrant to its bottom. A screw thread is 

 cut on the rod opposite the point where connection is made to 

 the city main. The upper half of the thread is left-handed, 



FIG. 301. Philadelphia high-pressure fire service. Vertical stream made 

 in underwriters' test. 



the lower half is right-handed. The upper, left-handed thread 

 carries a left-handed burr; the lower, right-handed thread 

 Carries a right-handed burr. To these burrs are attached 



