Mirro timeline...
The first Mirro Matic was introduced shortly after WW2, in late 45 or early 46, this has square handles screwed into an aluminum piece that was riveted to the pot, about 1948 or 1949 the handles that are on my cooker were introduced, this did away with rivets onto the pot, then about 1958, a little different handle was introduced, instead of the top handle ending in a smooth point, the handle now turned up slightly at the end and was squared off, all of these cookers were model 394, and you can no longer get the gaskets for them...I buy them anytime I see them, usually at old hardware stores and occasionally at estate sales.