81-133 bearings?

A contractor from sw fl says:
What type of bearings are in the 81-133?
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Dave from SWISCO responded:
The 81-133 Alcan Sliding Door Roller has sealed ball bearings.
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81-133 : Sliding Door Roller, Alcan
81-133
Price: $13.85
Sliding Door Roller, Alcan
How to maintain a sliding glass door
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How to maintain a sliding glass door