baseplate

Short definition from Wiktionary

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.
2. 2
   Synonym of tie plate.

Verb

1. 1
   To fit with a baseplate.
2. 2
   To provide (the vehicles within a fleet) with license plates registered as a batch in a particular state.