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Buy Genuine BBQ and Gas Grill Parts for Masterbuilt 20051214. It's Easy to Repair your BBQ and Gas Grill. 32 Parts for this Model. ✓ Parts Lists, Photos, Diagrams and Owners manuals.
Not a Masterbuilt, but I converted my GOSM. I used this hose and drilled out the orofice.
You'll want to double check and make sure those are the correct threads for the MB, but I think they are.
I don't recall the size of the bit I used, but there are resources available on the web - possibly here - that will give you the size based on original BTU and size. Let us know if you need help finding those.