A kara is a single continuous circle of iron or steel with no clasp, no hinge and no join, which means it is forged as one piece or bent from a single length and closed rather than assembled from parts, a deliberately unadorned object next to jewelry that could carry a clasp or a stone.
Material as statement
The choice of plain steel or iron rather than gold or silver is itself part of the object's meaning within Sikh teaching, which discourages ostentation, and a kara is not meant to be valuable as metal, only as the article of faith it represents, one of the Five Ks required of a baptized Khalsa Sikh, though many Sikhs and people of Punjabi heritage wear one as an identity marker regardless of formal initiation.
Wearing it, and what happens when it comes off
A kara is generally worn continuously and for life once adopted, and there is no everyday ritual for removing or replacing it beyond ordinary practicality, a bent or broken one is taken to a smith for repair or replacement rather than treated as scrap metal to be discarded casually. Some families keep a kara that belonged to a deceased relative rather than reworking or selling the metal, treating it as a personal object more than as bullion.