A bearing, extra spacers, o-rings, well just about everything you need to fix any Duncan bearing yo-yo except the Freehand MG, The Metal Zero 2 and the Profire (mind you, you can use this kit to upgrade the Profire for ball bearing play). Keep in mind, since this fits about every Duncan yo-yo, there will be extra parts when you replace the insides of any particular yo-yo, but more is better right? This kit does not include the threaded rods or nuts.