HORSESHOEING. 



11/) 



from the middle towards both ends. On the ground-surface of 

 the shoe the hole is moderately counter-sunk (Fig. 101), so that 

 after the thread has been cut and the calk screwed into place 

 the shoulder of the latter will rest on the counter-sinking. 



At present nearly all screw-calks are made by machinery, 

 either of iron or toe-steel. The former is too soft and therefore 

 not sufficiently durable ; the latter, however, is quite durable 

 when the calk is properly hard- 

 ened (tempered) by heating to a ^i«- 102. 

 cherry-red, sticking the head of 

 the calk as far as the tap into a 

 bed of moist sand, and allowing 

 it to slowly cool. 



The chief requirements of a 

 good screw-calk are, further, a 

 clean, deep, but not too coarse 

 thread, and but one size of thread 

 and tap for all calks, so that every 

 calk will fit in every shoe. A 

 calk whose tap measures one- 

 half inch (12.7 millimetres) in 

 diameter is sufficient for the heaviest shoes. In the German 

 army the calks used have a tap fifteen thirty-seconds of an inch 

 in diameter. The coachman should be given four calks (sharp 



Sharp screw-calks with Whitworth thread 

 (half-inch, natural size). 



Fig. 103. 



End of branch of shoe provided with a blunt screw-calk. 



and blunt) for each shoe, and a small screw-calk key (Fig. 117) 

 for placing and removing them. Screw toe-calks are also used, 



