While less common in the United States, English style Past Master aprons often contain embellishments made with chains. These are said to have their own symbolism, usually coming in groups of seven, with each chain containing seven links.
This is thought to allude to the seven liberal arts and sciences, each ending in a ball / globe. There are many instances where the number seven comes up in natural science and esoteric tradition as well.
Masonic aprons can contain a wealth of symbolism, even in the smallest detail!
(Thanks to Keith Mackinnon)
