A plant connector
From the chain
Rings  3mm
A clasp
From the extension chain

To begin, measure your wrist and subtract the value from the connector.

Divide the measurement in half then cut 2 pieces of chain.

Connect the chains on each side of the connector with 3mm rings.

Finally, cut a 3cm extension chain then connect the clasp and the extension chain.  at the ends of the chains  with 3mm rings.

And there you have it! Beautiful creation!