Im not sure i understand. Every cup i have seen, has them built into the cup.
If your making your own, any non neo mag will do,( Neo mags are a wee bit strong) which you can pick up all over the place. I found that Hobbycraft carry quite a huge range.
you're like Yoda.you dont say much, but what you do say is worth listening to....
Greg Wilson about.... Me.
I recommend that you buy a set of chop up balls and then get the right strength to suit the chopped ball Test it first to see if it atracts through a piece of wood/metal that will be similar in thickness.
Each cup and all set that you buy is slightly different so it will pay dividends to experiment a little.
Member of the Magic Circle & The 2009 British Isles Close-Up Magician of the Year
It's not really an optical illusion - it just looks like one!