This design work is provided by Milan Zahradníèek showing a special aerodynamic nut for the inside of the MGA Twin Cam intake manifold. This change requires a slight counterbore and drill inside the manifold, reduction of length of the threaded stud, and the special nut. See engineering drawings below.

The pictures below show an alternate approach. The picture on right is a standard manifold with the drilled hole for the stud and spotface to seat the flatwasher and self-locking nut. The picture on left is from the manifold on Robin Barker's Twin Cam YD2 2574 which was one of the five cars prepared for the 1960 Sebring race by the factory Competitions Department (but not raced at Sebring). This one has a counterbore to accept a socket head cap screw (Allen screw).