Index housing having a shallow spiral and the wire ends burring up against a stop require a flat bottom ferrule, or other flat stop. Otherwise, the conical bottom of most ferules, and fittings causes the wires to squeeze together and try to extrude though the hole.

While you see a plastic ferrule, which wouldn't address this, you don't see a steel plate at the bottom which take the load from the wires, an is usually made with a reverse cone (imagine a volcano shape) which drive the wires out and away from the hole.

Depending on the details, you might get by using a simple washer with a hole only big enough for the wire. Or they do offer the right type of ferrule for sale, but that depends on the ID of the stops.