for Specification difference , please visit this link:
In Short Words , the CPU is different for both Redmi Note 4X and Redmi Note 4.
in this articel , we will mainly introduce the difference for appearance
Back: Redmi Note 4X has a slim and bright line , Note 4 no bright line, a little whide
Bottom: Redmi Note 4X has 5 holes each side for speakers while Note 4 has 6 holes , and Two screws on the bottom
Edge: Redmi Note 4 has bright line on edge , Redmi Note 4X no bright line
TOP: the position of Remote Control is different. you can not use same case because of this position different.
Front: it is nearly same for Redmi Note 4X and Note 4 , so you can use same screen protector .