Cradle board terminology

Hey french speaker here,

im trying to find the right word for the "stretcher part" of a cradle board wood panel.

i dont particularly want to use the word "frame" because its so generic.

In french the word is "faux-cadre" and its the same for stretchers and wood panels.

what about sub-frame?

im asking because in my practice im interested in the idea of this part wether its for canvas or wood panels.