The flat surface where the washer and nut sit. It must be thick enough to resist bending.
This article dissects AISI E 1-16 (or latest edition) Volume II, Part VII, explaining its requirements for cold-formed steel framing connections and, more importantly, how adhering to this part of the AISI specification elevates anchor bolt chair design from a mere spacer to a critical load path component. aisi e 1 volume ii part vii anchor bolt chairs better