This is a MMZ (Momentan Zeit Zunder) - a military fuze  http://en.wikipedia.org/wiki/Fuze

It may contain explosives. The Swiss army has to clean up after exercises in the mountains, but don't always manage to do so. It  is probably best to turn it in for investigation/destruction.

Gwen is of course quite correct, and far more specific than I could have been.

However, I should like to add a few comments that, though you might not need them, some other people picking up unexploded ordinance might well need.Knowing that an explosive device has survived rough handling, such as being dropped from thousands of metres up, or fired from a gun, is no guarantee that it isn't just about to explode. Please never try to demonstrate how harmless it is by dropping, knocking, or heating it, or fiddling with the settings or movable parts of any such object!

For one thing, all it takes to stop such a device from exploding is the most trivial interference with its mechanism. The mechanism can start again, either because a bit of shaking has jarred the stoppage loose, or because it finally has slipped loose.

But, you might object, this device is too corroded for any such component to have survived in working order. Yes that may be true, though you cannot be sure, and it isn't worth finding out whether you are wrong, but it isn't the whole story by a long shot. That very same corrosion may be the slightest vibration away from releasing something that so far had been held safe by metal that had not yet corroded.

Not convinced? Well then what about this? (And I promise you, I did not invent this; it is a standard hazard for any disposal expert dealing with old unexploded ordinance):

Various chemicals, most notoriously picrates, but by no means only picrates, react with various metals, such as metals used in brass, to form explosive salts that are far too sensitive to be of any use in ordinance. They can go off from the merest knock, or from the friction of adjusting any screw setting, such as the calibrations you may see on that fuse head of yours. Do not, I repeat not, under any circumstances try adjusting it! You would be lucky to lose no more than your hands.

Put that object gently in a safe place, such as on a soft base in a hole in the garden, with a heavy plank or the like preventing any human or animal from going near it. Then have someone keep an eye on it from a distance while you call the authorities.

Congratulations on your good luck (and good sense) so far. If ever you find any other such object, mark the spot clearly, don't touch it, and call the authorities.

Good luck for the rest too.

Jon

Just to reinforce Jon's point about the unpredictable nature of explosives...

My father used to tell a story about how, in his youth, he arrived in time to stop my uncle - his younger brother - from blowing himself up. He and a friend had found a stick of explosive in a local quarry and had climbed a tree to drop bricks on it. By some miracle the sweating dynamite refused to go off. I've often wondered whether the anecdote was spiced up over the years, but the basic story was true.

Lacking my uncle's good fortune, a boy at my school blew his hand apart by trying to tamp a mixture of weedkiller (presumably sodium chlorate) and sugar into a copper pipe. It's not uncommon for teenage boys to underestimate the dangers of things that go bang.