Get something like these (an example from Amazon but see all the other types listed there). The plastic screw-on caps are only needed if you use bare wire. The plugs will mount directly into the backs of the speaker posts.
Monoprice 10 Pair Right Angle 24k Gold Plated Banana Speaker Wire Cable Screw Plug Connectors (121915) Black/Red https://www.amazon.com/dp/B071LK46PD/ref=cm_sw_r_em_apan_glt_fabc_HZA3GC3MT4GSZND1JXQV?_encoding=UTF8&psc=1
The amp is a Line 6 Spider Valve Mk II 112 Tube Combo and the converter I'm looking at purchasing is this