BSPP G1/4 barbed hose fitting for hoses between 5 and 7mm of Internal diameter. It has a small recess to fit an O-ring with 17mm of external diameter and a maximum of 2 mm thick.
The barbs larger and smaller diameters are, respectively 7mm and 5mm.
To be printed with the threaded side upward, using supports, to ensure the O-ring recess face flatness.
Thread length 9mm.
File identified as BSPP G1:4 5-7mm.stl

UPDATE 27/Nov/2021
-Added a 1 mm chamfer at the base for strength reasons.
-Added a smaller diameter version, under the name "BSPP g1:4 reduced", for less flexible or smaller diameter hoses. For this new fittings barbs larger and smaller diameters are, respectively 6mm and 5mm. There are two iterations of it available with 7mm and 9 mm of thread length.

UPDATE 13/Dec/2021
As the thing is gathering a significant success, i uploaded several designes with the most usual G1/4 sizes used for water-cooling. Those include fittings for 8mm, 9mm, 10mm (3/8''), 12mm (7/16''), 13mm (1/2'') hoses. The Internal hole diameters of the fittings are respectively 5mm, 6mm, 7mm, 7.8mm and 7.8mm. All the designs have 7mm of thread length. The remaining specifications were kept.
For all this new fittings, the small external diameter is 0.2mm below their identification size and the larger diameter 2mm above.
The thing name was also uploaded.