http://www.marinedepot.com/JG_1_4_i...s_Plumbing-John_Guest-RO5411-FIRORARP-vi.html[/QUOT
That fitting may work if you added an O-Ring to seal the body but its not designed as a true bulkhead seal. A second method I have used is to use a bulkhead cable seal in 3/8 size and a stem to barb adapter works great.
Jim
This is going into glass I assume? If so I'd suspect an oring on the wet side would work provided the hole was sized properly.
If you are going into plastic/acrylic then just drilling and threading the plastic with an npt tap will work.