Capillary tubes
Tiny breather tubes some makers add to a sealed glass unit shipped to high elevations, to equalize pressure so the panes don't bow or stress the seal.
What it means for you
A niche detail, mostly relevant if glass is made at one altitude and installed at a very different one. In most of NC it won't come up; if it does, it's a legitimate engineering feature, not an upsell.
Where you'll see it
On spec notes for high-altitude orders; uncommon on standard NC jobs.
Related terms
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