This is Discovery Plus Four  interconnect cables, purple in color and they come with Discoveries Audiocrast adjustable RCA plugs.  The Plus Four cables are I believe the best sound wise cables they make.   They are pure copper conductors.  I have several pairs of them all about the same and they are sonically excellent in sound.  Joe DePhilips really made a great pair of cables.    I think back then when he was making them he was using the copper that came from Butte mines which were considered the purest copper since they were smelted at the huge Anaconda Smelter in Anaconda, MT.  It was the worlds largest smelter and used a four stage process for getting out the impurities in the copper ore.  Then they must use a  Tin Baths in which the copper wires are cleaned by the tin baths enough to get rid of any contaminants in the copper.   Actually its a acidic tin baths.  I use to work in a wire plant and that is what they did to clean the copper of all impurities in the copper wires as it went through these baths they rinsed in water before coiling them on spools.     The sleeves on these plugs are adjustable for snugness.  They screw back and forth to do this.