Double series angular contact ball bearings have a similar design with single series angular contact ball bearings having two rows of balls arranged in opposite directions. The difference of double series contact bearings is that they can bear axial loads in both directions. They differ in the size of the contact angle and the design of the rests. Bearings are available in open and sealed versions. Due to the use of manufacturing technology, open ball holes can still have convenient indents on the outer ring for gaskets or screens. Sealed bearings don't need to be maintained and as a result allow exceptionally economical bearing structures. The self-aligning capacity of angular contact ball bearings is very small.