The Oakley Full Metal Jacket (FMJ) is a highly coveted, expensive, and awesomely limited production watch. It is also a color or coating on many different frames (ie. XX, Eye Jacket, Straight Jacket) which also several variation of colors (ie. FMJ +, 45mm, 5.56, 7.62, 9mm, Red, White, Copper, Gun Metal).
Oakley XX or Twenty is a frame that covered two Genereations with many colors. First Gen - XX (O-Review) Second Gen - New Twenty (O-Review)
The Oakley 5 3.0 is a completly different frame that is the third generation frame of the Five series which has technically 6 generations. The first 3 gens are very similar to each other and the last 3 gens are very similar to each other. Fives - O-Review Fives 2.0 - O-Review Fives 3.0 - O-Review Fives 4.0 - O-Review Fives Squared - O-Review New Fives Squared - O-Review