This is a red insulated binding post. These binding posts do accept banana plugs, and are a great way to connect single-wire leads. The colored cap screws up and down, and is designed to clamp on the connecting wire.
These binding posts are sold individually. We also carry a similar black binding post.
Based on 1 ratings:
Hard to seat and don’t lock on to boards and hold as you tighten. Connection was buggy until I overtightened it, worked in the end, but not well.