Linear Slider Issues

When I try to slide the metal shaft through the side of the linear slider it won’t work because the top part of the linear slider is blocking it from going through. What am I doing wrong?

Not sure what you mean by the ‘linear slider’. Do you mean the rack gear? Can you post a picture?

Thank you for answering! By linear slider I mean pieces like this

linear slider.PNG

This video might be helpful to you:

Thank you so much! That helped