Abstract: A boom is mounted for pivotal movement about two orthogonal axis. Rotation about the horizontal axis is provided by a sealed boom pivot bearing utilizing a floating bearing pin in an oil filled enclosure. Vertical loads and side thrust forces are accommodated by a second sealed bearing utilizing a bearing post received in a cylindrical bearing enclosure. Vertical thrust is absorbed by a sliding bearing relationship between the bottom of the bearing post and an end plate on the cylindrical enclosure. Side thrust is accommodated by a sliding bearing relationship with the walls of the enclosure. A supplemental vertical thrust bearing is provided at the upper end of the cylindrical enclosure.