"Pressure canners for use in the home were extensively redesigned beginning in the 1970's. Models made before the 1970's were heavy-walled kettles with clamp-on or turn-on lids. They were fitted with a dial gauge, a vent port in the form of a petcock or covered with a counterweight, and a safety fuse." - 'Using Pressure Canners', Elizabeth L. Andress.
"Pressure canners for use in the home were extensively redesigned beginning in the 1970's. Models made before the 1970's were heavy-walled kettles with clamp-on or turn-on lids. They were fitted with a dial gauge, a vent port in the form of a petcock or covered with a counterweight, and a safety fuse."
- 'Using Pressure Canners', Elizabeth L. Andress.