Furutech terminal blocks have been developed with the aim of satisfying the most demanding consumers.

They are made in Japan from pure copper and Alpha treated (cryogenization + demagnetization).
The advantage of copper over brass is better conductivity as well as higher magnetic resonance frequency.
Brass is easier to machine but its resonant frequency is 22kHz, which is very close to the audio spectrum and can cause unpleasant auditory sensations.

These terminal blocks are also available in gold plating.