Bed leveling knobs with locking nut for the Ender 3.
Dimensions remixed to match the stock knobs with a slot to insert a nyloc nut (to suit hardware available in my region specifically). You may need to scale to fit your own nuts.
Edit (V2): revised to reduce the contact shoulder offset (distance of the knob from the baseplate once mounted) along with a deeper nut pocket. These changes increase the available range of travel on the threaded bed rods once installed, simplifying install and allowing maximum adjustment.