We were given a Frigidaire dryer that was converted to propane. We have natural gas. How can we convert it back to natural gas?
What size does the orifice need to be? It is 55 now, can it be drilled to make it a bigger size?
The copper plug that it has right now has a white needle. Do we need to get a different plug?

I would start at Frigidaire and try to get a manual. It usually tells you how to converet. If that doesn't work, go to a propane dealer or a good hardware store-NOT HD or LOWES> . They should be able to give you conversions. I have an Ace near me that can do it. HOWEVER the orifice is not the only thing you will need to change. You will need to change the pressure regulator. Some regulators have built in conversion in their regulators. Again, check the manual. I have an AMANA and the regulator has a spring loaded pin on the diaphragm. One side is LPG one is NG.

Here is the kit they put in. to convert it to propane.
http://www.partselect.com/PS862368-Frigidaire-PCK2003-Natural-Gas-to-Liquid-Propane-Conversion-Kit.htm?SourceCode=1&SearchTerm=fdg336res1&ModelNum=fdg336res1

Same site get the kit to convert it to Natural gas.
Do not just change the orifice it will cause a fire. The burner needs to be changed to a natural gas burner. Also the igniter needs to be changed. It all comes in a kit for about 30 bucks.