GROIN VAULT

Definition: 

Where two barrel vaults intersect perpendicularly. A single arch connects each pair of neighboring arches, and another larger arch connects each pair of diagonally opposite corners. Each of four triangular quadrants formed by these two crossing arches is vaulted in what is roughly a barrel vault.

GAUGE

Definition: 

A unit of measurement traditionally used to describe the nominal thickness of steel. The lower the gauge the greater the thickness.