The muzzle of the exploding bolt stands one inch off the pin when in safety position, that is, when the safety key rests on the brasswork of the priming case. This can always be ascertained before entering the bolt (if thought necessary) by a wooden gauge forced down until it touches the point of the pin, which measurement transferred to the bolt will show the distance of the muzzle when forced down to the safety position. The safety key is secured in the slot of the exploding bolt by eight or nine parts of strong whity-brown thread secured to the key, as shown in Fig. J (p. 10), passed round the bolt, and securely knotted in this manner; the parts of the thread come away with the key when drawn, in order that none of the parts may be worked down the tube by the exploding bolt. [Illustration: (I)] [Illustration: (J)] In the event of the large torpedo being cut away in deep water after withdrawal of the safety key, it will explode by pressure on the head of the bolt at about sixty fathoms depth. The small one at about thirty. The brass guard for the exploding bolt is an extra precaution (suggested by Capt. A. Hood, R.N., Director-General of Naval Ordnance) should any person by mistake attempt to place the bolt into the torpedo without the safety key in its place. It is placed over the head of the bolt and pushed down until the thumb-screw on the side works into a small hole in the shoulder of the bolt.[1] The manner in which this guard is fitted ensures its removal before launching, since the after lever cannot be placed until it is. It also makes a convenient handle for turning the bolt in the magazine. [1] As the certainty of explosion depends mainly upon the exploding bolt being properly charged, the inventor takes entire charge of this important detail. [Illustration: (K)] The explosive composition in the bolts is powerful and safe; so packed that no amount of concussion can explode it; the bolt must be pierced through the capsule at the muzzle for that purpose. The bolts are hermetically sealed at the muzzle by a metallic capsule, and can be stored for an indefinite length of time without chance of deterioration. The exploding point of the composition in the bolt is 420° Fahrenheit. [Illustration: (L)] The side and top levers are so arranged, that when driven close into the torpedo, the bolt is down to the shoulder; and, since there are three explosions to take place, it is calculated the torpedo will be in hugging contact when the main charge explodes, and exploded by a powerful discharge in the centre, thereby disposing of the explosive force to the greatest advantage.