The VakPak65™ system uses 309 stainless steel foil to mimic the results of vacuum heat treating. Used by metal tool makers around the world, these lightweight containers heat more rapidly than the work piece. As a result, the undesirable elements in the entrapped atmosphere react with the container long before the work piece is hot enough to be damaged by them.
The container acts as a protective barrier, not just during heating, but throughout the entire hardening and quenching operation.
Measurement across includes the welds. Fact this into your size selection.