Milwaukee 49-66-6709 SHOCKWAVE Impact Duty 3/4” Drive 4” Extension The Milwaukee 49-66-6709 SHOCKWAVE Impact Duty 3/4” Drive 4” Extension provides you with better access in hard to reach places and offers extreme impact durability in high torque applications. Our laser-etched size markings allow for fast identification of drive size and length. The dual-hole design and ring groove allow you to easily attach and remove the extensions. All Milwaukee® SHOCKWAVE™ Impact Duty™ Socket Extensions are backed by our Lifetime Guarantee and meet ASME industry standards.