Screw-down holders clamp your card to hold it — and a quarter-turn too far leaves a mark that never comes out. The Calyx well is cut a breath deeper than the card is thick: it's held by geometry, not force.
Optical-grade acrylic with no haze, no tint, no lens effect at the edges — centering, surface, and foil read true through the case. It also filters ~99% of UV, so the card you show off stays the card you pulled.
Every figure below is measured, not marketed. If a number matters to you and isn't here, ask us — we like collectors who check.