This is the standard (as opposed to firm) Brompton suspension block assembly (complete with bolt and fittings)
Suspension is important on small wheeled bikes such as the Brompton.
The suspension on a Brompton is provided by a polyurethane block mounted between the main and rear frames.
Lightweight and effective, it smooths out the lumps and bumps and helps to avoid excessive bounce.
Two levels of resistance are available, to suit body weight and riding style.