A planetary gear hub assembly (1) comprising a housing (2) with a planetary sun gear (3) rotabably mounted in the housing (2). The planetary sun gear (3) meshes with a set of planet gears (4) which also mesh with a ring gear (5). A thrust bearing (25) is mounted on an outer end cover (7) of the housing (2) for engagement by an outer end of the planetary sun gear (3). The thrust bearing (25) is formed by a wear pad (26) mounted on an inner face (27) of the end cover (7) and an associated wear plug (28) mounted in a central axial bore (29) at the outer end of the planetary sun gear (3). An oil passage (30) extends through the wear pad (26) and communicates between an interior of the housing (2) and an oil-filling port (32) during normal use. The plug (34) can be removed for checking the oil in the housing (2) without affecting the position of the wear pad (26).