Hi Boyd,
LonePhantom is quite right. I just wanted to add that the wiring should be as follows;
For a stereo / three pole jack; tip=hot (red), ring=cold (blue), sleeve=shield (usually either braided wire or simply a third wire without any covering).
If you hold the jack so it's pointing to the ceiling then from top to bottom would be Tip / Ring / Sleeve.
If the cables have different internal colours ex. orange, yellow & braided then make sure the wiring is the same at both ends of the cable and you'll be fine.
For a mono / two pole jack; tip=hot (red), sleeve=cold (blue). There is no centre 'ring'.
Again, as long as the wiring is the same at both ends you'll be fine.
You can use three core cable on a mono jack by either;
A. not soldering the braided cable to any contact but make sure it is insulated so as not to touch or short out with another cable, or
B. solder the second (blue) and third (braided ) cables to the sleeve contact at both ends of the cable, effectively making the cable act like a two-core cable.
Do not use a two core cable in a stereo jack! That's just going to confuse some poor bugger trying to find out why he or she can't get signal!
One more thing - I use several cables with the Neutrik Silentplug and depending on the socket you are plugging it into it may or may not work 100% of the time. Fine for me to use for practise sessions or in a studio but I wouldn't dream of handing it to a musician at a live gig! Just passing on some experience from a sound engineer's perspective.
Good luck!
Edit; here is a handy link to see different cables & connectors and how they are wired.
http://www.mediacollege.com/audio/connection/
