There are plenty of options for a manual Z axis adjustment knob for a cupcake, but I haven't seen one for a mendel yet. I'm still getting my mendel up and running but wanted to manually move the Z up and down a bit.Print it out and screw it straight on to one of your Z-axis threaded rods. You may have to shorten the M4 bolts going through the z-bar-top-clamps if you have them fitted. Heck, do one for each threaded rod for bonus points!Mine turned out plenty tight enough, but I guess you could add a grub screw if yours is a bit loose.