The 401k represented another major innovation in yo-yo technology, as we've come to expect from the Van Dan Elzens. Hans and his team at YoYoFactory created the first yo-yo with an adjustable response system. Shuttles around the bearing move in or out, depending on how you adjust the knob on the outside of the yo-yo. So response can be increased or reduced, depending on how you advance or retract the shuttles.
While the 401k came with starburst response, stickers could be also used, making this a very flexible design. Look carefully at the shuttle around the bearing, and adjustment knob on the outside.
