Bearing adapters for use with truss foundations supporting mechanically balanced single-axis trackers. The bearing adapter joins the free ends of a pair of adjacent truss legs to form a rigid A-frame shaped foundation structure. A bearing is formed in an upper portion of the bearing adapter to allow a torque tube to be suspended from a pin in the bearing and to swing through an arc bounded by the bearing adapter. The bearing may have a catenoid shape to compensate for misalignment in multiple directions.