You glue magnets on the inside of your vest. This way is more forgiving and quicker than putting permanent holes in your vest or sewing on some velcro since you can just pop off the magnets and re-glue them to the appropriate spot. It's just preference really and magnets, velcro, or whatever method you come up with that will securely keep your armor in place on the vest will work for 501st approval. Just make sure the magnets you use are strong enough. I use Neodymium Magnets 1/2 x 1/8 inch Discs. Each of those magnets have a pull force of 6.1 pounds which is plenty for holding your armor to the vest. It has its pros and cons like any other attachment method. I would look at other methods also to find which you'd prefer.