A classic mechanical watch is an investment. At least, that’s what you tell yourself – and your significant other – when they question why you want to spend thousands of pounds on something your smartphone does.

But it’s a lot more than that. A proper timepiece is also a rite of passage. When you become a man, you put away childish things like the Spider-Man Swatch and the Casio calculator watch (unless you’re styling yourself like a late aughts hipster) in favor of something that syncs with your adult status.

For that reason, a watch is something that fathers often pass onto their sons when the latter turns 18 or the former dies (or he just wants an excuse to buy a new, even more expensive watch).

If you’re investing with a view to bequeathing, then you want to avoid anything with even the faintest whiff of fashion. (This rule also applies to wedding photos.) Think ‘classic’. Think ‘iconic’. But don’t think ‘timeless’, because we’ll slap you in the face for using the oldest cliché in the watch-describing book.

Unlike you, these five pieces of grown-up wrist candy are guaranteed to still be stylish when your rugrat is legally allowed to buy you a drink. You could put whichever one you choose in the wardrobe to appreciate untouched until their 18th. But then it does seem a crying shame not to make use of it…

(Related: 5 watches that will only go up in value)

Cartier Tank

As its moniker suggests but its elegance most certainly does not, the Tank was inspired by the WWI battlefield weapons that at the time – 1917 – were considered as revolutionary as its namesake timepiece’s square shape.

“Cartier’s Tank has evolved into various versions over the ages but the original is still the best: not too big, not overly cluttered, a perfect representation of the Art Deco period that spawned it,” says Chris Hall, deputy editor of specialist watch magazine QP. “Whether the associations with WWI tanks are of genuine importance to the design is somewhat moot – for nearly 100 years it has been the perfect square watch.”