Gold-filled technique consists of a base metal such as brass or copper, to which a sheet of gold is bonded by pressure or other means.
To qualify as gold filled, an article of jewelry must have a layer of gold at least 1/20th, or 5% of the weight of the entire article.

Closed links.

A large oval link followed by 1 small oval link.
Length of a large oval link: 3.7 mm.
Length of a small oval link: 2.2 mm

Sold in one piece, by multiples of 50cm.