Barb Fitting M6

I modeled this after the fitting that you can get from aliexpress. it has o ring already in it and M6 thread and the hole is 2 mm at teh smallest end. the barbs are 5 mm in diameter and and the smaller outside diameter is 4 mm- This fitting is marketed as "M6 Male Thread Mini Tube Hose Barb Air Pneumatic Pipe Fitting Connector Adapter Coupling". Tihs size option was marked as (M6-6mm) even though it also says "-6: Max Outer Diameter: 5.15mm" s oI think 4-5 mm tube is more appropriate for this fitting. I think this is nickle plated brass as they are marketing this as Brass fitting.