Clarification; If the material is carbon steel (because the post is under D1.1) there is no need to machine anything down to 1/8 inch. The side bends would be 1/2 (thick) X 3/8 inch wide, with the 3/8 inch being the thickness subjected to the bend. If face and root bends are performed (again, assuming the material is carbon steel) the face bend would be reduced to 3/8 inch thick by removing material from the root surface and the root bend would be reduced to 3/8 inch by removing material from the face surface.
If the material is aluminum, and M23 base metal or F23 filler metal is used, the face and root bends would be reduced to 1/8 inch thick in a manner similar to the carbon steel (just more material is removed).
Kix isn't wrong, I just thought the explanation could be more explicit.
Best regards - Al