From the manufacturer:
Atom Bionic Swiss bearing feature titanium ball bearings and utilize shields to protect the internal parts of the bearing against contamination by dust, and liquid. The shields help contain the lubricant in the bearing, are fixed to the outer ring and have a non-rubbing seal to the inner ring.
Sold as a 16-pack only, for 7mm or 8mm axles.
Order the 7mm version for axles on Roll Line plates.