The ETI-Research BP-20C Binding Post is a very high-performance binding post at an entry level price. Made from 1100 series Hardened Copper with an IAC Rating of 102% you can be assured that the audio signal is not being degraded having to go through a poorly conductive material such as Brass.
The BP-20C has a Gold Plating applied without any nickel. Many manufacturers use a nickel surface applied before the Gold Plating as this makes the Gold have a shiny look. The unfortunate problem is that Nickel is a poor conductor and will degrade the Audio Signal!
The Housing is made with a Aluminum over a Polymer compound. The Polymer threads onto the Post as to not have any conductive material touching the Pure Copper. The Aluminum is great at rejecting EM/RF noise that is so prevalent now days.
Also your choice of securing the wire by either the screw or solder.
The Post length is 20mm which is the preferred length for Chassis mount or in certain Speakers Back Playtes
The Nut used to secure the BP20C is made from a high-density nonconductive Polymer so that no conductive material is touching the Copper Post except for what is needed to transfer the Audio signal.