Start using the Quick Change countersink system, and you’ll wish your drill bits were quick change too. With these innovative adapters, they will be. A spring steel collet in each adapter securely grips the bit when the nut is tightened. That means you can use a range of drill sizes in each adapter - important if you use letter, number, or metric series drill bits. Most important, if you happen to break a bit (it can happen) just loosen the collet, insert the good half, and continue working! Individually, the adapters do not include the drill bits - purchase those separately. Fractional size 3/8". Number size B. Metric size 9-1/4. Made in the USA.