Unfortunately, my speaker jacks are round, otherwise I would use an inch pounds tork wrench to
tighten.
For newbies, over the years, I have found banana, spades etc to be inferior to direct speaker
wire connection. Bypassing the jacks and soldering the speaker wires to the OPT leads is the
best of all, but I need flexibility to remove the amps for testing purposes.
Whether wire, banana, spade etc, it is important that the surface be completely straight and smooth, with
no slight kinks or even tiny, rough spots that would reduce the contact area, increasing the resistance.
Increasing the resistance lowers the damping factor across the entire audio band.
cheers
steve