The fixing device includes a base including elements for pivotal mounting of the ring; a foot carried by the base, including a first pair of lugs extending from the base, a crossmember disposed between the lugs, and a second pair of lugs connected to the base; and a rod adapted to enter a bore provided through the base; each of the lugs having a shoulder over the whole of the width of the lug, the shoulder forming a transition between a first section of the lug and a thinner second portion. The support includes the above device and a ring retained in the pivotal mounting elements.