These new eccentric nuts are a revision of the standard eccentric nuts that have been a part of the Shapeoko 3 from the start. These HD Eccentric Nuts feature the following: * A larger bearing surface to reduce deflection as the nut is tensioned * Deeper threads * Longer neck to reach deeper into the steel axis plates The HD Eccentric Nuts are sold as a 9 pack, enough to swap out all of the nuts on your Shapeoko 3 and still have an extra to lose somewhere on the ground in a corner. Note: Starting January 2020 all Shapeoko CNC routers began shipping with HD Eccentric Nuts as the standard option. So, there is no need to upgrade if you purchased a machine in that time frame.