This is a second attempt to create a useful locking mechanism for the MakerGear M2's Z-axis knob. The first version, http://www.thingiverse.com/thing:873378, does not allow the M2 dual extruder carriage to move all the way to the left. This version stays clear of the extruder carriage in all positions while keeping the feature of releasing itself if the Z stage is homed while the lock is still in place. It has the additional feature that the lock handle can be placed upside-down on the cap and makes a convenient handle for hand-cranking the Z stage. Updated July 22; knob now has a small overhang at the top, which helps stop the lever from twisting in the locked position, and also helps keep the level from slipping out when using it as a hand crank.This knob works only with the low-profile Z-axis knob that comes with the dual extruder upgrade for the MakerGear M2. It comes in two pieces, a knob cap and a handle. Both print without issue, although the knob cap will need support. The knob cap gets placed over the Z-axis knob, and can stay in place more or less permanently, as it does not interfere with any of the parts of the dual M2. The handle has a hole that fits over the pin on the knob cap. To lock the Z-stage, place the handle so that it points downward on the left side of the frame. The weight of the Z-stage will cause the handle to hit the side of the frame, preventing any further drop. If the Z-stage is lifted, either by homing the Z axis or homing all axes, the handle will be pulled off of the cap, automatically unlocking the Z stage. The handle can be placed on the knob cap upside-down to make a convenient handle for hand-cranking the Z stage when the motors are disengaged.