Usage of "symmetrical" and "symmetric"

Merriam-Webster lists symmetric as being a variant of symmetrical, which is the 'official' dictionary entry:

symmetrical, adj : 1 : having or involving symmetry : exhibiting symmetry : exhibiting correspondence in size and shape of parts : BALANCED, REGULAR {the human body is symmetrical} {crystals are often symmetrical} {a symmetrical garden} {a symmetrical grouping}

"Symmetrical" is a non-technical term, to describe any object that has symmetry; for example, a human face. "Symmetric" means "relating to symmetry", and is also used in a number of technical mathematical contexts (see Sam Lisi's comment under the question).

I suggest that items may be symmetric in appearance; therefore, they are symmetrical. Ex: My hands are symmetric in appearance; therefore, they are symmetrical.

Perhaps when speaking about one item as a whole, it is "symmetrical" (meaning that both individual sides are similar to one another); however, when speaking of both parts individually, they are "symmetric" to one another.