an equator 25 which lies in a horizontal plane and is disposed adjacent to an annular peripheral wall portion 27 of the housing 11 of ball transfer unit 10 the housing 11 of the ball transfer unit 10 additionally comprises an annular retaining ring 29 positioned within the housing 11 parallel to the equator 25 of the conveyor ball 14 and above the ball bearings 24 so as to generally confine the ball bearings 24 to the mounting surface 26 the conveyor ball 14 rests upon the concave support surface 30 so as to contact the ball bearings 24 at an annular load zone depicted schematically at 32 in fig3 the existence of the annular load zone 32 permits slight movements of the conveyor ball 14 when the unit 10 is under load conditions it should be appreciated although too small to be depicted in the drawings that in accordance with conventional practice the conveyor ball 14 contacts said ball bearings 24 only in the region of the annular load zone 32 under both no load and load conditions of the ball transfer unit 10 and that there may be a slight spacing between the conveyor ball 14 and the ball bearings 24 in areas outside this annular load zone 32 the annular seal 18 comprises an annular body portion 39.