These mate with one another (in the obvious male-to-female chain). They seem to be male-to-female banana plug adapters. Maybe I am being naive, but these seem useless. What are these useful for in practice?
EDIT: They do not come apart, i.e. they are not banana plugs waiting to be soldered to wire.
The only thing I can think of is that they're intended to be connector savers.
Best Answer
They look like they are adapters for shrouded banana plugs. As far as I can tell from your photograph, the red plugs have bodies which narrow after a ridge and the black ones have a uniformly narrower diameter. The narrow bodies fit inside the shrouds of the shrouded plugs.