12 STD refers to the axle size/bearing size of a wheel. As of right now, all 12 STD wheels are 120-125mm in diameter, and 30mm in width. This larger shape accompanied with the larger bearing makes the wheel much faster, and more durable. If you have an Ethic deck, double check to see if it is 12 STD compatible, because this is definitely something you want to try out! This fork DOES come with conversion spacers to run 24mm wheels, so even if you're not ready to upgrade to 12 STD, pick this fork up so you have the chance to in the future.