When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
One looks like this "X" and one looks like this "H"
That about covers it. BUt since this site is full of smart asses like myself i will explain for the noob.
An H pipe is two pipes side by side with a pipe in between to balance out exhaust flow etc.
An X pipe actually brings the two pipes to one intersection then back out again for full exhaust intermingling
here's my knowledge on the subject. they both bring balance to the flow of you exhaust system. x-pipe is actually more effective than the h-pipe because the h-pipe becomes virtually ineffective above 3000 rpm. x-pipe keeps the balance throughout the entire powerband.