How to Convert old propane grill to new propane tank?

Generally speaking, the male POL fitting on the regulator should thread into the internal female threads of the new bottle and may not need to be changed out.

An old propane grill can be converted by removing the male POL fitting from the inlet of the regulator and replacing it with a new female QCC-1 adaptor. The new adaptor is available at your local propane company and they will remove and replace the fittings for a fee. You can see this at http://fireforless.com/.