Belt: An endless loop of flexible material between two rotating shafts or pulleys.

Press: an Apparatus comprising of one belt and two anvils.
see picture:
http://www.htracyhall.org/History/Photos/belt.htm
more pictures:
http://www.htracyhall.org/History/bio.htm

In 1954, the G.E. diamond team headed by Tracy Hall, Senior, became the first on record to produce synthetic diamond by a witnessed, revealed and, most importantly, reproducible process.
Hall was responsible for the development of the "belt press," a high pressure, high temperature apparatus, which was a key element in synthesizing diamond from carbon. Indeed, he later developed two other types of press for the synthesis of diamond: the tetrahedral press and later the cubic press.
http://www.gemlab.net/publication1.htm