older iron work had different sizes than now.
It depends on how you define "now." Items like waffle irons and handled water pots did have some changing numbering schemes in the latter part of the 19th century. Round griddles seemed to be more like stove eyes with handles, so they followed standard stove eye sizes.
For the trivets, I doubt that you’ll be able to tie an unmarked trivet to a foundry. The 2 designs that you posted were reproduced by many companies like Wilton, John Wright, Lodge, JZH, Virginia Metal Crafters, Art Smithy, and that’s just off the top of my head.
Your photo IMG_1140 is called Eagle and Heart by collectors. Lodge called it Eagle Laurel Trivet.
Your photo IMG_1141 is called Oder of Cincinnati by collectors. Lodge called it Sunburst Trivet.
Trivet names aren’t too standardized as you can see.