No 3U in The following editions which are very popular! Iso 800,600,200 Cab 21, Cab 20 and most cab series of rackets. If at all u have seen a Iso 800 3U then It is a Big time fake!
Check http://www.yonex.co.jp you will find that ISO800 has 3U version. And I actually saw such racket in a Yonex retailer shop and for sure it is genuine. It has everything the 2U version has. But to be honest, 3U version is not common at all.