These propellers have been working pretty well for me / us, they've taken a lot of abuse and most are still in one piece. These propellers come in two different varieties. The carbon composite props are lighter, stiffer and can spin faster without falling apart. The colored, glass fiber filled props are a bit more flexible which can be helpful if you have a habit of cashing into hard objects. Adapter rings with IDs of 3, 4, and 5mm are also included. Sold in pairs.