Red boot to suit genuine Neutrik 1/4" connectors (either 2 or 3 pole). Use it to ID your leads - it's made out of the same 'unbreakable' stuff that ships in black as standard with your Neutrik Phono. Also fits NP2RCS & NP3RCS.
Note - this is the retro boot, to suit old-style Neutrik NP2C or NP3C.
For the full range of Neutrik boots to suit current connectors, check the BPX series