Stainless steel plates measure aprx 6" x 3.5"
Production date scratched onto one: "2-3-89"
Recently removed from a 1989 Cal Spa Supra model, see last photos for reference (along with other components also available separately in our store).
The 31-year old hot tub in question was in exceptional condition with little exposure to the elements within an enclosed space

As shown with coatings of redwood stain and age wear