Small Box Hinges

[Lbob131]

Does anyone know  how  the 1/4  stop quadrant  is engineered  into the  hole  to give an accurate opening  angle of 92 degrees?

I think the stop quadrant will  only be in  the outer part of the hole. It also needs to be  an extremely tight fit  on the inner knuckle.
Splines?
Such a simple device  but  an amazing piece of engineering.
£29  pound per set.

Is EDM  CNC  machining involved?

 

[JSlovic]

I'm guessing they broached the hole.  Brass is relatively soft and the process provides a very accurate hole geometry.