Converting single speaker terminal to tri-terminal

I have an amp with single speaker terminals, I would like to add two more terminals as I have tri-wire speakers and a sub that connects via speaker level inputs.

Planning to make a copper plate that I can attach like a spade with two holes on the side to to connect two additional terminals. The existing terminal has enough clearance to prevent the new terminals from hitting the back cover.

My question are.
1. Is copper the best material for the plate?
2. Do i need to have the copper plated?
2. How thick would the plate need to be ?
 

Attachments

  • speaker terminal copper plate.png
    speaker terminal copper plate.png
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Stacking dual banana plugs will not work, the wires are too thick and heavy to be stacked, The wires are AWG 11 x 6 per channel. Don't ask why 😀 I just have too much wire on my hands 🙂

The easiest thing to use would be stacking dual banana plugs, but they are fixed at 3/4" spacing
(and your amp is not 3/4"), so you'd have to stack single banana plugs.
These would be suitable: Blocked