I also use Wray's discs. They are GREAT! And if you buy the set with the small and large disc it comes with a GREAT video on using a shrinking disc. It REALLY shows how the theory works as well as the proper use of a shrinking disc.
Can't go wrong for $100! Best money I ever spent!
http://cgi.ebay.com/ULTIMATE-SHRINKI...ht_2797wt_1139