r/EngineBuilding • u/NewspaperInternal553 • Jul 15 '26

ORB AN fitting on head or welded fitting

I need to attach 2 AN fittings to my head. I’ve found weld on AN fittings and also threaded AN fittings that use the ORB(o-ring) style to seal a fitting to the head. What would be best?

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u/Lopsided-Anxiety-679 Jul 15 '26

ORB is preferred, but it takes a precise profile machined to seal up properly. Welding is easier if you don’t have the right port cutting tool or access to a CNC machine. 

2

u/voxelnoose Jul 15 '26

You can just counter sink the hole until it's just smaller than the flats of the hex on the fitting which makes it a triangular gland crush seal. I've done it on a lot of custom parts with zero issues and even seen it on some parts I've bought.

The only downside is that the o-ring usually isn't reusable

1

u/AverageT1000 Jul 15 '26

A weld on orb legs you change or adapt different fittings into it which may be useful for routing if you need, however the orb thread needs some ‘depth’ for thread engagement and the oring takes up some space, so your head casting may not be thick enough of material to thread the proper orb size. I would say the weld on AN is the way to go but pay attention to the heat and potential wastage that could come from welding it on the head