Summary

Scriber, 150mm long, carbide tip. 

Detail

Designed to 'scribe' on metal (e.g. silver, gold copper), but also used as a scratch-test for those that are too mean to spend money on a diamond tester - because most (not all) gemstones can be scratched with a carbide tip whereas diamond cannot.

For testing uncut stones: if you can scratch it, it's not diamond; if you can't scratch it, it might be diamond.

For testing cut stones:

a) draw the tip across customer's precious gemstone, if it scratches it, it's not diamond

b) the customer sues you for damaging their precious gemstone

c) even if there's nobody to sue you, you have just damaged a gemstone and it is now unsaleable.

Is it easy to use?

Yes.

Limitations

Stones (including diamonds) are not necessarily the same hardness in all directions.

Once scratched, a polished gemstone is damaged and probably becomes worthless.

Scratching a gemstone can cause it to crack.