Luristan. The rigid single-piece mouthpiece bar, secured by bent back ends, is also unusual; elsewhere more flexible mouthpieces are found. Many pieces have small spikes on the reverse of the plates; it is thought these were either used to control the horse, or to fix backing pads of softer material. Pin heads Large decorated pin heads are the third common and distinctive type of Luristan bronzes, falling into two distinct groups: sculptural and openwork designs, many using the iconographic repertoire of other types of objects, and flat, normally round, disk heads. Their use is uncertain; they were probably both used as votive offerings, as the numbers found in the excavated temple at Surkh Dum suggests, but also worn as decoration or for fastening clothes. Other uses have been suggested. These have not been found in excavated tombs. Pin heads in bone and faience were also found at Surkh Dum. The disk-headed pins are made from sheet metal by repoussé and chasing work, engraving and other techniques, so differing from the types described above, which are cast. Many designs centre on a large face, and in general humans predominate over animals in their decoration, another difference to the other types. The diameter of the disk is typically between 6 and 9 centimetres, and the whole pin and head up to about 20 centimetres. Similar large face designs are found on some other plaques of uncertain purpose. The faces are mostly rounded to fill a circular space, and may be intended as female. They lack beards, and some full figures are clearly female, sitting with open legs displaying a vulva, perhaps shown in childbirth; in other pins this is clearly the case. These pieces were presumably votives for fertility. The eyes are sometimes inlaid in white, with a black dot for the pupil. The face may occupy most of the disk, or be small, at the centre of a wide border with other subjects. Other designs feature a wide range of subjects, with some purely decorative motifs, and others featuring some complex, mainly religious, scenes with many figures ("odd-looking demons and animals apparently involved in cultic and mythological activities", as Muscarella describes them). Other types Other types include bronzes centred on a large ring, mostly decorated with animals in way similar to the finials and cheekpieces. These perhaps were part of horse-harnesses. Large socketed pieces are assumed to be handles for whetstones.