Blank where wheel could be for the 87-162?

A quick learner from Irvine, CA says:
July 13, 2022
Why is there a blank where an paired wheel could be installed?
Do larger windows require both wheel locations be populated with steel wheels?
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Tom from SWISCO responded:
July 20, 2022

The 87-162 roller is only ever meant to use one wheel at a time. The reason why this assembly (and many others) have a blank wheel slot is not to accommodate a second wheel, but to change the height of the wheel it already comes with. If you look at our photos more closely you'll note that one slot is higher than the other. This is allows for a rudimentary form of adjustment in case your sash needed to sit higher in the track.

Please note that this is also described in the 87-162 product description.

Side view of 87-162
Side view of 87-162
Sliding Window Roller, 5/16" Flat Wheel
Sliding Window Roller, 5/16" Flat Wheel
87-162
$2.75
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