Into the finished and concentric bore of our projectile is now forced a cleverly and home-designed expanding mandrel, a taper mandrel in fact, which expands a hollow (and again concentric) bush, and on this the base is centred. Transferred to an adjacent engine-lathe the shell is fixed on a shorter three-bush expanding mandrel, and turned to the correct and finished diameter. Removed to a turret-lathe, a slight operation of counter-boring the mouth is performed; this is necessary, as medical practitioners may be astonished to learn, for the purpose of receiving the nose. The mouth is also faced, and screwed, but screwing is effected on another instrument of torture, styled a thread-milling machine; so prior to lifting the shell from the turret-lathe a recess is cut in the far cavity of the mouth, this forming a clearance for the thread-milling tool. The turret of the lathe having no transverse travel, an ingenious little tool was designed and fixed into the turret-head by means of which a transverse travel, actuated by a hand-rachet and sufficient for the required depth of the recess, was obtained. Anything which is at all conducive towards the saving of time, especially in war, is _ipso facto_ a device of the utmost strategic and economic value. "Ask anything of me but time," once said Napoleon, "it is the one thing I cannot give you." So, in the case of our thread-milling machine, the saving of time effected is considerable. The shell is as incomplete without the screw-thread in its mouth, as it is without its nose; the thread has to be cut somehow; and by the employment of a milling-machine and thread-cutter the job can be done in about ten minutes as against an hour or more if done in an ordinary screw-cutting lathe.