This is a hexagonal key.
The openscad source is provided, so it can be modified to be another size, with a bigger handle, etc...

In particular, the tolerance can be modified, so the key is slightly smaller in order to make sur that it fits. The provided key is 0.2 tolerance (-0.2 mm on all sides of the key so it is actualy 11.6mm instead of 12mm).

The size and the tolerance are printed on the handle.

Note: I did not print this model yet. As soon as I get the chance to print it, I will comment on how I did.

I made sure the overhangs are 45 degree max, so it should print easily.