Model created in Zbrush. It is watertight and ready for printing/milling. Although there are some undercuts, it was created with molding and casting in mind.Includes a file of the cross merged with the skull and also the skull and the cross separately, in case You'd like to cast them in different materials.

Nominal size (although easily adjustable in any 3D software) is:

30 mm wide/ 40 mm tall /2.9 mm deep/ volume: 0.65 cm3