HilleRange 2120, 3120, propane hose connection size?

[Eastward ho 24]

I think I have a hilleRange 2121 or 3121. Can't find any numbers. I've run 3/8 soft copper to the galley. Now I need to apply the stove. I thought it was a 5/16 nipple on the back of the stove. However it seems they don't make 5/16 propane hose,or 5/16 to 3/8 reducers. I hoped to terminate the 3/8 soft copper with a flair nut and put a 3/8 to 5/16 reduceing nipple then to a prefab 5/16 l.p hose. But seems not the case. Any one know where I'm going wrong? I'm not at the boat to double check my measurements

[Eastward ho 24]

P.s it's brown 3 burner stove...