Adapter Retention Resolved

The replaceable insert was always the strategic core of CORVO-001 — it is what keeps the knob from being locked to one car. It was also, for the entire Rev A program, the largest unresolved question. Earlier concepts were explored and deliberately rolled back rather than approved, because a retention mechanism that fails is not a cosmetic problem.

The resolution decouples the two jobs the joint has to do. Torque resistance and pull-out resistance are different loads, and trying to solve both with one feature is what made the earlier concepts fragile. Anti-rotation now reacts through a hex form-lock; axial retention is carried by a single screw. Each joint is mechanical, positive, and does exactly one thing.

Anti-rotation is a Ø16 mm across-flats hex on the adapter, mating a broached hex pocket in the knob body. Torque passes through the flats. First-order sizing puts the governing limit in the 6061 body bearing against the flats rather than in the 17-4 adapter itself — the aluminum is the weaker half of the joint, which is the correct place for the limit to sit, because it is the half whose geometry we control.

Axial retention is an M6 12.9 socket head cap screw entering from below through the adapter flange into a captive tapped boss in the body, with roughly two diameters of thread engagement in 6061. Backing out that one screw releases the adapter for a swap. That is the whole service procedure.

Why hex, and not the alternatives. A Double-D or two-flat interface concentrates bearing load on two faces; six flats distribute the same torque across three times the bearing area in the aluminum, which matters because the aluminum is the governing side. A hex broach is also standard tooling with predictable tolerances, and it indexes at 60° increments, so an adapter can be seated in six orientations without a preferred clock position. The earlier keyed and clamped cartridge concepts asked one feature to resist both rotation and pull-out, and required custom geometry to do it. This is more boring, and boring is the specification.

One thing to be clear about: the physical Rev A prototype already ordered predates this decision. It does not have the hex pocket or the tapped boss. It is still exactly the right part to receive, because its job was always to answer questions about exterior geometry and hand feel — questions this change does not touch. The retention architecture will be proven on a later part.