Speaker binding posts with plastic covers

people are telling you their experiences with their connectors that do unscrew, like mine .....

the type you posted DOES NOT unscrew. read the full description

another spade to banana adapter, 

I sent an email to Krell yesterday. Their response: "They just unscrew." So I'll have to just unscrew them. I'll try some channel lock pliers. Do you think a blast of Deoxit might help loosen it? 

@rfprice 

Now that you unscrewed them once, they should be good. And I don’t believe Deoxit has any lubricants in it.

All the best.

I have similar situation and all I did is just busted plastic covers leaving metal screw caps. They don't hold up tight and within the time they will twist off.

Later I've replaced them with brass nuts

@curiousjim Deoxit F5 is specifically designed for switches and has lubricant. Any other Deoxit is also similar to penetrating oil 

Don't use solder on speaker wire, for the same reason you don't use it on 200A electrical connections.  It makes the wire brittle and is low conductivity. Always crimp.