Wire drawing die

A wire drawing die having

• (a) a core formed of polycrystalline diamond having no variations in hardness properties, made only of diamond and produced by:
• directly converting into diamond a starting material of (i) a non-diamond type carbon material with a grain size of 50 nm or more and (ii) a non-graphite type carbon material or a finely pulverized graphite added to said non-diamond type carbon material;
• and sintering the diamond at an ultra high pressure and an ultra high temperature without adding a sintering aid or a catalyst,
• said polycrystalline diamond having a mixed construction including fine-grained diamond with a maximum grain size of less than or equal to 100 nm and an average grain size of less than or equal to 50 nm and plate-like or particulate coarse-grained diamond with a minimum grain size of greater than or equal to 50 nm and a maximum grain size of less than or equal to 10000 nm, and
• (b) a hole configured in the core to permit passage of a wire material to be drawn through said hole,
• wherein said polycrystalline diamond has a construction in which layered or relatively coarse diamond crystals are dispersed in a matrix of fine-grained diamond.