On a Brompton M type Handlebar there is not a lot of space to install cycle computer, smartphone, front light etc.
This extender bridge, crossbar takes place in the middle of the handlebar. You just have to snap it firmly onto your handlebar. The engraved B must facing you when you're on the Brompton
You can add double sided tape to fix the extender.
Diameter is standard 22.2mm.
Disclaimer: Do not grab this bridge to pull/lift the Brompton, or add a heavy handlebar bag onto, it was not designed for that.
This extender doesn't fit the older Brompton M handlebar (before 2017).