Hex Shank
Affiliate link — we may earn a commissionA hex shank is a six-sided bit shank, usually 1/4-inch across the flats. Impact drivers use a 1/4-inch hex collet instead of a traditional chuck, so they only accept hex-shanked bits. The flat sides prevent the bit from spinning in the collet under high torque. Hex-shanked drill bits and driver bits are sold everywhere. You can also put a hex-shanked bit into a standard drill chuck, but not the other way around. Round-shank bits don't fit in a hex collet.
Why It Matters
If you own an impact driver, you need hex-shanked bits. They're the only kind that fit. One-handed bit changes take about a second. Keep a set of hex-shanked drill bits alongside your driver bits so you aren't stuck without the right shank type.