Hello norcalwelder, that sounds like a Victor tip designation number. If you want the exact pressures that Victor recommends for that tip you can likely Google the Victor website and find that information out. I don't have ready access to my charts at the moment.
      Also consider the 1/7th rule when you are looking to operate this heating tip, if you're unfamiliar with this, it has to do with the draw-off rate for Acetylene from various capacities of bottles. Acetylene can only escape from a particular size of bottle at a specific "Cubic Feet Per Hour Rate", if you exceed this rate you will start pulling the acetone out of the bottle and risk ruining the hoses and regulator components. Each tip size has a CFH consumption rate that can be mathematically compared to the size of bottle that you are using to see if it is safe to use. I'll give an example: if you have a large commercial type acetylene bottle that has 350 written on the outside of it, that indicates the contents of the bottle, dividing 350 by 7 will equal 50, the 50 would indicate the CFH consumption rating that could safely be drawn from that cylinder. As long as the tip you're using requires less than 50, the bottle will support the use of that tip, if the tip that you try to use has a rating greater than the 50 in this case, you would need to manifold an additional bottle or bottles together until the CFH rating for the bottles was greater than the consumption of a particular tip or application. This is something that many individuals out in the trade or dabbling in welding aren't readily aware of. Hope this has helped some. Regards, aevald

From Victor lit. #6 MFA-J should run at 8-10 PSIG Acetylene & 10-15 PSIG Oxygen. The fuel consumption will be from a min. of 14 CFH to a max. of 40 CFH. If the tank pressure drops way off, or the flame getts funny colored, or the tip pops and gets hard to work with You are over the 1/7 rule for sure.