Dado style eggcrate return
Eggcrate air returns without rounded edges can be used for sidewall returns (as shown), or also as retrofits for broken floor units as often seen in craftsman bungalows and well as other house styles. Larger sizes often require extra structural support as well as fiddling with shims in order to make the piece flush with the surround floor. It is not a bad idea to have some measurements handy when you call for a price quote . . .