Squeeze is the compression that makes an O-ring seal: the fraction of the cross-section diameter W taken up when the ring sits in a gland of depth L, computed as (W − L)/W × 100. Static radial seals want roughly 15–30% depending on the section — the verified Parker Design Chart 4-1 glands deliver about 22–32% for 0.070 in cross-sections down to 15–20% for 0.275 in, smaller sections needing proportionally more squeeze because tolerances eat a bigger share of a thin ring.
The honest evaluation runs at the tolerance extremes, not the nominals: a skinny ring at the low end of its AS568 cross-section tolerance sitting in the deepest allowed groove, and a fat ring in the shallowest. For a -214 (0.139 ± 0.004 in section) in the chart’s 0.111–0.113 in gland, that spans 16.3% to 22.4% — inside the printed 16–23% band. Machining to the handbook’s gland depth lands the squeeze in the right band automatically; the squeeze check exists to show where in the band a real toleranced assembly can actually land. Face seals and dynamic reciprocating glands run different squeeze regimes on their own charts.