Problems with list combinations in Python

I have some Python lists of information that I want to concatenate. These lists are similar to these:

vars1 = ["x1", "x2"]
vars2 = ["y1", "y2"]
main_list = ["a","b","c","d"]

What I want is to get all sorts of combinations (even I do not know the correct operation name) to cover all cases that I bring up:

    ("x1,a,x2", "y1,a,y2"), ("x1,a,x2", "y1,b,y2"),
    ("x1,a,x2", "y1,c,y2"), ("x1,a,x2", "y1,d,y2"),
    ("x1,b,x2", "y1,a,y2"), ("x1,b,x2", "y1,b,y2"), 
    ("x1,b,x2", "y1,c,y2"), ("x1,b,x2", "y1,d,y2")
    ("x1,c,x2", "y1,a,y2"), ("x1,c,x2", "y1,b,y2"),
    ("x1,c,x2", "y1,c,y2"), ("x1,c,x2", "y1,d,y2"),
    ("x1,d,x2", "y1,a,y2"), ("x1,d,x2", "y1,b,y2"),
    ("x1,d,x2", "y1,c,y2"), ("x1,d,x2", "y1,d,y2"),

I have researched itertools.product Function, but I can not get the desired result 🙁

I would be glad if you could help me. Have a nice day!