A stand‑alone brake fluid reservoir used in motorsport or custom brake systems where the master cylinders are mounted remotely (typically on a pedal box inside the cabin or under the dash).
Instead of being integrated into the master cylinder, the reservoir sits separately and gravity‑feeds fluid down to the cylinder.
Because it has a threaded bottom fitting, it provides a secure, leak‑resistant connection and is compatible with most racing pedal boxes that use threaded feed ports.