>>9379599 lb
It's just Masonic symbolism
3 holes in the skull
2 ends on one bone
2 ends on the other
That adds up to 7
But, the X of the crossed bones plus 3 of the skull equals 13
And then we have the Plimpton 322 tablet shown here...
https://blogs.scientificamerican.com/roots-of-unity/dont-fall-for-babylonian-trigonometry-hype/
Pythagorean triples
Math, geometry, astronomy
Those crossed bones are the X and Y axes
And the skull is the Z axis
If you used a bone or a line for the skull
You would have a 6 pointed star
Like the one in the center of this 3D cube