Reproduction of a hair needle (acus) has a head shaped like a hand, the neck has an annular shape and the head joins the body of the needle is coiled. In the Roman world they were used exclusively by women, although at first they were also used by men when it was still fashionable for them to wear long hair. The sizes and types of decoration depended on the tastes and purchasing power of each woman.

The headdress was a fundamental element of adornment for the Roman woman, sometimes they reached a large size and were authentic works of art, which is why it is believed that they had a slave dedicated to hair and makeup called ornatrix. Women always had to present themselves with their hair up, as loose hair was a disqualifying element and was considered a trait of abandonment and neglect.

Hair pins could be made with antler, bone or bronze, but there were also others made of more noble materials such as ivory, gold or silver. Dyes were sometimes used for bone acus, mostly red or green. In most cases these needles were used to collect hair, there are few cases in which they have been found related to other uses, but other utilities such as to hold clothes are being considered.