The X-12 lug nut socket size to choose for the Alpine Coach is 1 5/16" or a nominal 33mm. The 1 5/16" socket does fit somewhat loose on the lug nut, but it works, and that is what the X-12 vendor recommended.
a. I measured my lug nut with a micrometer which read 32.75mm. So, 33mm is a bit large.
b. 1 5/16" = 1.3125" = 33.3375mm. So, 1 5/16" is also a bit more too large.
c. However, 32mm would be too small.
d. The closest fit would be 1 19/64" = 1.296875 = 32.940265mm. I don't think you can buy a socket in this size for a lug nut.
The X-12 can be used on the rear wheels. See these pictures I took with my X-12 attached to a lug nut of a rear wheel of my 2006 Alpine Coach: