you can crush any d grade item to get d crystals, and you can get an idea how many crystals you get from each item from the official website, library section. you dont want to buy a d grade item just to crush though, unless taxes are 0% or you are really in a pinch. only crafters 20+ can crush d grade items. if you get your crafter up to about level 30, you can use haste pots to train the bots who are spoiling ol mahum raiders. with some luck you can get 100+ leather boot linings or 50+ bone helmet designs from a single train. when the bots forcelog take the opportunity to spoil the ol mahum raiders yourself, and manor some blue codas to get leather. craft all the leather boots you can, then crush them (i think they are 38 crystals each, they take about 4 leather, one high grade seude, and one d gem to craft, which is a lot cheaper than the store will sell them to you for). as you get to higher levels, other mobs may spoil parts for better d grade items. stick to gloves and boots, as they take the least amount of materials to craft and the parts spoil very easily.