A draw bar for a retractable screen arrangement in which a screen material is extensible across an opening by movement of the draw bar in an extension direction in order to screen or partially screen the opening, and in which the screen material is retractable by movement of the draw bar in a retraction direction, to reduce occlusion of the opening by the screen material and in which the screen arrangement applies a retraction force, in the retraction direction, to the screen material, to assist retraction of the screen material; wherein the draw bar comprises: a brake arrangement for providing a braking force between the draw bar and a bearing surface of a track which in use guides the draw bar to resist relative movement of the brake arrangement and the bearing surface in at least one direction, the brake arrangement comprising: a brake member which provides a friction surface for contacting the bearing surface; a brake member support for supporting the brake member; and a forcing arrangement for forcing the friction surface against the bearing surface; wherein the forcing arrangement comprises: a biasing arrangement for biasing the friction surface towards the bearing surface, and a force increasing arrangement for increasing the force with which the friction surface engages the bearing surface, characterized in that the force increasing arrangement is configured to increase the force with which the friction surface engages the bearing surface by converting at least some of a frictional force applied between the friction surface and the bearing surface into additional contact pressure force applied to the brake member to increase contact pressure between the friction surface and the bearing surface, and in that the force increasing arrangement comprises a forcing part having a first region connected to the brake member support, a second region connected to the brake member, and an intermediate region for transmitting force between the first region and the second region. a brake member which provides a friction surface for contacting the bearing surface; a brake member support for supporting the brake member; and a forcing arrangement for forcing the friction surface against the bearing surface; wherein the forcing arrangement comprises: a biasing arrangement for biasing the friction surface towards the bearing surface, and a force increasing arrangement for increasing the force with which the friction surface engages the bearing surface, a biasing arrangement for biasing the friction surface towards the bearing surface, and a force increasing arrangement for increasing the force with which the friction surface engages the bearing surface, characterized in that the force increasing arrangement is configured to increase the force with which the friction surface engages the bearing surface by converting at least some of a frictional force applied between the friction surface and the bearing surface into additional contact pressure force applied to the brake member to increase contact pressure between the friction surface and the bearing surface, and in that the force increasing arrangement comprises a forcing part having a first region connected to the brake member support, a second region connected to the brake member, and an intermediate region for transmitting force between the first region and the second region.