baseplate

/B EY1 S P L EY0 T/
noun
  1. 1

    A solid piece of material that has enough strength and sturdiness to serve as the surface to which other things are attached to be supported.

noun
  1. 1

    A steel plate used on rail tracks between flanged T rail and the crossties.

Synonyms

Source: https://en.wiktionary.org/wiki/baseplate, https://en.wiktionary.org/wiki/tie%20plate