You have got the wrong part. You either have an extruder intended for 30mm hole separation but your x-carriage is designed for 24mm hole separation, or the opposite.
This part is for helping you adapt one to the other, either temporarily while you print a replacement part or to keep it.
It may work both ways (just remember only two nuts are needed).
You will need M3 screws of proper length so they can be screwed to the nuts inserted into the part without protruding to the back of the part. Once you have checked the adjustment, remove this screws and used another pair of M3 screws to screw the part to the x-carriage, next attach the extruder to the new part that now is securely fixed to x-carriage.