Includes 26 Centering Rings in 5 different sizes. BT5, BT20, BT50 and BT55. Perfect for making your own engine mounts! 26 Centering Rings 8 each. BT5 to BT20. 4 each. BT5 to BT50. 8 each. BT20 to BT50. 2 each. BT20 to BT50 - 1 inch long. 4 each. BT50 to BT55.