a pearl of mother-of-pearl
 a flat-headed nail 
 un pendentive 20mm
 a 4mm ring
 of the extension chain
 of the very fine chain
 3mm and 4mm rings
 a buoy clasp

It's very easy to assemble: start by mounting the mother-of-pearl pearl on the nail and forming the loop.

Tip: don't make the loop too small because the chain will have to slide through it.

Then mount the pendant on a 4mm ring.

Cut a very thin piece of chain about 45cm / 50cm long. Adjust the size as required. Widen the links with a reamer to make it easier to fit the rings. 

Thread the pendant and pearl onto the chain.

Then at the ends of the chain, place the clasp with a 3mm ring on one side and a 3cm piece of extension chain with a 3mm ring on the other.

Beautiful creation!