In the centre of the priming case is a brass tube in which the exploding bolt works, and at the bottom of this tube is a steel-pointed pin, which pierces the capsule on the muzzle of the exploding bolt, when the bolt is forced down. At the side of the brass tube, and near the base of the pin, is a small hole, covered with thin brass foil, which will allow of an escape of water into the priming case, should any have collected at the bottom of the tube. The loading hole of the priming case is at the bottom of the case, and arranged with cork and cap upon the same principle as the loading holes for main charge. A powerful spanner is provided for screwing in the priming case and caps of main loading holes, which are fitted with leather washers to form a water-tight joint. The priming case can be stored separate from the torpedo if preferred, but there is no necessity for so doing unless it is charged with a dangerous compound. When the torpedoes are being stored, a wooden plug is inserted into the brass tube of the priming case; there is a cavity in the plug at the lower end; the cavity is filled with a greasy composition, into which runs the pin of the priming case when the ping is in its place; the pin is thus protected from corrosion, and the tube of the case secured from any foreign matter getting accidentally into it. The exploding bolt is fitted to work with a pressure of about 50 lbs. on the head of the bolt for the large torpedo, and 20 lbs. for the small. [Illustration: (F)] On account of the great proportional length of the stuffing box, it is quite impossible for water to enter into the tube, and the pressure can be regulated to the greatest nicety by the quantity of thread wound on. The bolts are easily kept in order by turning them round occasionally in their tubes, stored as they would be in the bolt magazine (see p. 20, Fig. Y). The best lubrication for them is hog’s lard free from salt, beeswax, neat’s-foot oil, in proportion 3, 1, 1. The bolt has several grooves for the thread stuffing to be wound on, and in the event of its working too easy, a few turns of whity-brown thread on the two lower stuffings will suffice; should it work too stiff, revolve it in the magazine tube until it works with the desired amount of pressure, which, after a little practice, is well known by the hand. In the event of a few drops of water entering the tube, which has never occurred, a provision is made for its escape (see priming case), that it may not impede the descent of the bolt. The cavity in the bolt for containing the exploding composition is, in length and diameter, sufficient to contain a charge that will of itself explode the torpedo (see Fig G), without depending upon the priming case. The bolts are all the same size, and differ only in the direction of the slot for safety key, being port or starboard bolts accordingly. [Illustration: (G)] [Illustration: (H)]