Rambam on Mishnah Kelim 12:1

A man’s ring: A ring made as an ornament for a person, such as a signet ring with an engraved design, leg-bands, and golden necklaces that kings make and wear around their necks.

An animal’s ring: Rings made for animals, as kings make rings of gold and silver for the necks and legs of horses.

Likewise, rings are made on the handles of utensils for decorative purposes; this is what is called a “utensil ring.” Such a ring does not become susceptible to impurity when it is detached.

The beam/shaft of arrows: A piece of wood into which the arrow is inserted; in their practice it has its completed form once the iron point is attached to it. This is why it was mentioned here.

“And [the chain] of prisoners”: It is placed on the leg of prisoners.

The collar (קולר): The iron yoke that they place around the necks of prisoners in order to restrain a person and the like. That is, it may also be used to bind together bundles of wood and similar things which are ordinarily tied so that they remain gathered together.

“Of wholesalers (סיטונות)”: Sellers of bread and flour have chains with which they secure their shops, and these are considered part of the locking mechanism. But the chains of private householders are not made for locking; rather, they resemble the chains made on gates for decoration, and therefore they are not susceptible to impurity.

Rabbi Yose says: If at its two ends there are two projections resembling a key—as though they also lock with this type [of mechanism]—or if a chilazon is attached to this chain, meaning the likeness of a creeping creature made of iron, with which they lock the doors; and this creeping creature is the aquatic creature called chilazon—[then it is susceptible to impurity].

The halakhah does not follow Rabbi Yose.