How to fill a 20lb BBQ Propane tank with LPG?
If I understand correctly you want to adapt a 1" P.O.L. to a 1-3/4 ACME so that you can fill your BBQ propane tank with a different connector.  

In that case you'd want something like this.



1-3/4" ACME to 1" POL Adapter

If you do get something like this, make sure it comes preassembled, or assemble carefully with yellow teflon or propane rated pipe dope.