5pc 4" Plastic Ball Shells

These are of 2 kinds: the ridge going in or going out, and they assemble tightly as these ridges interlock into perfect 3.75" diameter spheres . I bought these for a purpose other than fireworks They seem strong enough but I might fill them with epoxy for even greater durability. A hard to find item because of the precision required to make such a hollow sphere. I can't imagine blowing these up!