As used on the new (introduced in 2024) Brompton 12 speed ultralight rear wheel.

This chain pulls the internal hub gear to actuate a gear change (don't pedal as you change hub gears).

Suitable for Sturmey Archer / Brompton 12 speed (3 speed hub) rear wheel.

The gear indicator chain comes complete with the locking nut which tightens against the cable anchor on the Brompton.