jax 6.11 onward
Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
with guinsoo's terrible nerf jax has suffered,so this build became really handy in this patch especially after the trinity's buff;the manamune is a great asset as it will cause much damage after stacked.
hextech gunblade is also mainly primal for his sustain as it will combo well with trinity,manamune,gandmaster's might passive,titanic hydra etc...
you might discuss the starting items as it is not-so common to see a doran's jax with also 3 quints of ls,but trust me,9.5% of life steal in the first part on laning phase,is just incredibly usefull when you dont want to lose cs
hope it helps