These clips are very useful for fixing the glass
(which is the 3d printing base) to the heated bed.
The movements of the axis that moves the heated bed may cause the cristal base to shift which can result in a bad printing performance. There are two ways to prevent this: the use of a silicone thermal pad
or 4 clips.
The option with the clips makes it very easy to remove the glass base for cleaning purposes.
Price per unit. 4 clips required to hold a base.