Independent means that each jaw moves independently. Such 4-Jaw Chucks are used for holding odd shaped pieces or where zero tolerance is required. This 6 4-jaw chuck with a 1-1/2 bore has semi-steel bodies and hardened reversible jaws. Requires a mounting plate. Note the mounting holes through the back of the chuck. This is because each jaw moves independently and there is no scroll in the middle. What’s in The Box. 6 Inch 4-Jaw Independent Jaw Chuck. 30 Day Satisfaction Guaranteed. Secure & hassle-free shopping. All our sales are backed by a 30-day satisfaction guarantee.