These are simple holders for the nut used to level your print bed.

The dialer is oversized to make it easier both to turn it and to turn it precisely - it is easier to make small adjustments to a larger wheel. On the CR-10 (the printer I own) the size makes it stick out from the support frame which makes one finger adjustments easy; just hook the tip of your fingernail on one of the ridges and spin it.

The locker is on the same screw and is used to lock in the dialer. Once you have the bed level hold the dialer with one hand and turn the locker until it is tight against the dialer. With this tension neither the dialer or locker will now move when being vibrated by the printing process.

These parts are sized for M4 or 6/32 screws and bolts. You can fit to smaller or larger sized simply by scaling the models in your slicer. You'll need 8 nuts to do all four corners of the print bed.