It serves the 9, 15, and 50 position shell sizes — one ferrule part number covers the three most common D-sub position counts in the HDP-20 family. The ferrule slides over the cable jacket before the contact is crimped, then gets crimped itself to clamp the cable braid or overall shield to the connector backshell. This is the inner ferrule — it sits closest to the contact, with the outer ferrule (a separate part) completing the strain relief and shield termination sandwich.
Why the Inner vs Outer Distinction Matters
The AMPLIMITE HDP-20 system uses a two-piece ferrule set: an inner ferrule (this part) and a separate outer ferrule. The inner ferrule is crimped directly over the cable braid after the contact is terminated; the outer ferrule then slides over it and is crimped a second time to lock the assembly. Using only the inner ferrule without the outer leaves the shield termination mechanically incomplete — the cable can pull out of the backshell under tension. The 7-745129-0 is the inner half only; order the matching outer ferrule (typically TE 745127-x series, position-dependent) for a full shield-crimp assembly.