The male fitting that inserts into the QC on the tailer is going to be a standard size. What is going to vary is the size thread that the QC fittings use. They are going to be either 1/4" or 3/8". Larger ones are used for commercial applications and do not apply here. As far as matching the fittings to the propane hose, you are going to see either NPT threads or swivel flair connections. There are adapter fittings available for both types.
The QC on Keystone trailers are made by Fairview and are available all over the Internet.
Read the stick I wrote on Grill conversion in the Modifications forum and it will be pretty obvious what you need to do. The photos are also very good, if I do say so myself..
There's also some info on Hansen and Mr Heater fittings that you will need to know.