XL chain 
 a locket clasp
 5mm and 4mm rings
 pendants

Ultra simple assembly:

Start by measuring your wrist and divide the value by 2.

Cut the 2 pieces of chain.

Open a link of the twisted oval chain to attach the oval chain, then close the link. This allows a simple and direct attachment without needing to add a ring.

Then place the clasp directly onto the chains.

To finish, place the astro pendant with a 4mm ring and the stone heart with a 5mm ring, being very careful not to damage the stone.

And there you go! Beautiful creation!