The one I use is homemade, and I think the hole is around .030, but am not sure as it has been several years since it was made. Mine also uses a hi-pressure regulator at the bottle, but have seen them used with out a regulator. If you have a small set of bits .030 could be a starting point and you can go bigger as needed.
Thanks for the input. I think I will try to make one out from aCast Iron Premium Venturi that I found athttp://www.tejassmokers.com/castironburners.htmand some 3/4" black pipe.Shortone Iwill start out with .030 holes in the pipe and try that.
The whole reason why I am doing this is because, I cut up my old brinkman charcoal grill and add a fire box to the side of it, add a full water tray in the bottom and make it a reverse flow smoker.
Ishfab, the one I built is a 1/4" pipe about 3' long with a piece of 1 1/4" pipe on the end to mix gas and air to burn. It has one single hole in the center of the cap for the 1/4" pipe. Mine is NOT a burner for the smoker, I use it to start my wood when smoking. I don't know what size to make multiple holes if making a burner.