My guess would be millilitres. I have metric measuring spoons, and the teaspoon is 5 ml, the tablespoon 15 ml. That would mean you have a half-teaspoon measure too!

I'm with @saucefiend. My measuring spoons are in millilitres too.

So you bought half-teaspoon, teaspoon, two teaspoons and tablespoon measures.

Thanks - I thought that's what I might have. Now, to remember what they are for future use...

Yep, another vote for millilitres.

Easy enough to remember 1 tbsp: 15 ml and 1 tsp: 5 mm; the rest are fractions.

Yes, It's millilitres.
A teaspoon is always 5ml. Curiously - in the US a tbsp is 15ml, while in several other countries a tbsp is 20ml.

Yeah, they're millilitres. The 10ml spoon is a dessert spoon. You don't really see it used that often nowadays though.

So:
2.5ml = half-teaspoon
5ml = teaspoon
10ml = dessert spoon (or two teaspoons)
15ml = tablespoon

Hope that helps. :)

Wow.

Americans actually don't know this??

That's a little terrifying.