| Ball bearings were invented for high speed operation (i.e. jet engines). The opening and closing of a door is not considered "high speed", and our TA self-lubricating, smooth-surfaced, oil impregnated bearings are meant for moderate speed, heavy load situations. Therefore, we furnish our TA (oil impregnated) bearing on all 5-Knuckle hinges as a standard with the exception of both 6" and 8" hinges which have ball bearings. The volume of 6" and 8" hinges does not warrant tooling for the oil impregnated bearing. |