The fuze model 16, which is used with 120 mm and 380 mm ammunition is in the shape of a truncated cone with screw-threaded adapter at base to screw into the nose of the sheel. The entire fuze – apart from the brass windshield at the nose, and base plug – is painted black. The overall length of the fuze is 7.9 cm, and the diameter at its widest part is 6.2 cm.

The steel outer casing is closed at the top by a brass cover plate or wind shield, fixed at the top end of a cylindrical mouthpiece by a brass ring positioned over the cover plate and fixed by indentations of the rim of the mouthpiece.

A brass base plug with central channel screwed (L.H.) into a brass bush it it-self (R.H.) into the base of a steel adapter screw threaded internally and externally.

The steel adapter screws internally into the base of the outer case for about 1 cm, and holds in position, by a flange at the top end, the aluminium housing to the brass cylinder block in which is found the mechanical shutter arrangement.

The brass bush is screwed at the bottom end of the adapter against the aluminium hous-ing and has a central cylindrical cavity containing creep spring and detonator adapter.

The detonator adapter is cylindrical, of reduced diameter at the top half, to carry the creep spring, the lower half being hollow and screw threaded to take the detonator hol-der, which is also cylindrical with a cylindrical cavity in the inner half to hold the detona-tor. This, too, is cylindrical and loose, being positioned when the detonator holder is screwed into the adapter. The upper half of the detonator adapter has a central longitu-dinal channel, down which a needle passes to pierce the detonator on impact or graze.

The aluminium housing is positioned on top of the brass bush, thus holding the creep spring in tension. It is fixed by a flange at the top of the steel adapter. The brass cylin-der block fits into the lower end of the housing and is positioned by a closing flange at the top end and fixed by a set screw.

The brass cylinder block contains the shutter mechanism and the components are shown in diagram "C". "C" shows the external appearance – a bottom brass cylinder surmounted by a brass positioning disc with a small central guide tube for the second connecting rod, two steel washers (C3) and a closing disc (C4) all attached to the main body by two screws. The central guide tube is positioned di-rectly above the flanged head of the needle supported by the flange on the U end of the horseshoe centrifugal bolt – see C2, C6 (longitudinal sections) and C/ (transverse section).

The shutter arrangement can be seen from C7 to consist of a centrifugal bolt with a small protruding lug on the inner end, working against a centrifugal spring, held in place by a screw plug. The lug fits into a hole in the side of one of the arms of the horseshoe centrifugal bolt so that until the centrifugal bolt is thrown out, the horseshoe centrifugal bolt and the needle are immovable.

The horseshoe centrifugal bolt is a cylindrical bolt, forked at the end and flattened at the top and bottom so that it cannot move in the channel. The whole of one side is grooved transversely to fit the teeth of the first cog wheel so that as the bolt moves the first cog wheel rotates. The drives a second cog wheel by an axial cog as shown in C6, and the second cog wheel drives a third, and the third a fourth in the same way, so that each cog wheel overlaps the previous one over quite a large area. The fourth cog con-tacts a stabilizing disc, which vibrates as the cogs rotate, i.e., as the centrifugal bolt moves outwards. When the bolt moves inwards the cogs rotate but the disc remains still.

Above the brass cylinder block and fitting to the cavity formed by the flange of the alu-minium housing, but separate from the latter by a brass washer, is a long aluminium guide shaped at the top end to fit the cylindrical mouthpiece of the outer casing and having a central channel throughout the length. Into the top end of the channel fits the rod with hammer head attached. Inside the channel is the first connecting rod of the same diame-ter, and below that, protruding from the guide, is a second connecting rod of much smal-ler diameter so that it passes through the small central guide of the brass positioning disc in the shutter block and emerges in contact with the top end of the needle suppor-ted on the arms of the horseshoe centrifugal bolt.

The channel inside the guide has a reduced diameter at the top half so that the hammer head can move forward, but not the first connecting rod, whereas they can both move backwards as on impact.

On firing, the centrifugal bolt immediately flies out leaving the horseshoe centrifugal bolt free to move out under the action of centrifugal force. If this were also to take place im-mediately, the needle would be released during acceleration and would set back on the detonator, thus causing a premature in the bore. To prevent this, the horseshoe centri-fugal bolt is controlled by the system of cogs. During acceleration, the cogs set back on one another and the friction set up between the comparatively large faces of contact is sufficient to prevent the bolt moving outwards. On deceleration, however, the cog set forward and separate, friction forces are small and the horseshoe centrifugal bolt can move out, releasing the needle, which, however, owing to set forward, reamins in its ori-ginal position against the second connecting rod.

The detonator holder at this stage tends to set forward but is held away from the needle by the creep spring.

On impact the impacting force is transmitted through both connecting rods to the needle which pierces the detonator.

In both cases, the flash is transmitted through the flash channel in the base plug to the exploder system.

Fig. 25 – Italian Fuze, Model 16