When mixing small mount of rhenium into tungsten in the tungsten pin making, it is rhenium tungsten pin. The reasons why add rhenium are follows.

Rhenium tungsten pin significantly reduces the brittle characteristics of tungsten at room temperature.

And the addition of rhenium increases the recrystallization temperature, the ductility, and the ultimate tensile strength of tungsten-rhenium alloys and decreases the ductile-brittle transition temperatures of tungsten-rhenium alloys.