Please help me find a source for the standard, common, interior dimensions of burial vaults in the u.s.a.?

I have built a casket according to plans obtained on-line. However, I need to be able to site a source for those who ask, " How do you know the casket you built will fit into the standard sized vaults used ?" I have spent about 45 min.s typing in every possible wording for, " burial vault dimensions ", in the search engine, and there is not one source that I can find. I keep coming up against this one company as a reference, [whose name shall go un-mentioned ] but they don't give the exact dimensions of the interior, nor any at all , for that matter. Any help in this regard will be greatly appreciated. Humbly, john