Ritual gifting was the basis of Viking society. Arm bands, necklaces and finger rings were given out by lords as marks of favor when the treasure hoard was distributed. The tradition is so fixed that "ring-giver" is an equivalent term for "king."
Arm and wrist bands were popular because they allowed one to show off the wealth they represent while keeping them safe. The bands weren't made of pure metals. Usually, a band would be made by twinning a golden wire around an iron rod, which was typical of Viking jewelry making.