2010 silverado. Just had a new windshield installed

After the work, i notice the wiper arm not sitting in the correct position. When i removed the arm to align it properly, I noticed a tappered shaft with splines, but it looks as if the inside of the arm itself where it mounts is not splined. Is this assumption correct?

Looks to me that i just align the arm where needed, then the splines 'dig in' as the nut is tightened on the taper shaft.

Is this correct, i don't want to wreck the splines if there are any, but it is hard to tell. ANyone have experience with this? I felt it with a screw driver, but it looks like an imprint mark only.

Thanks