P40 wing washers ?

I have noticed on a number of airworthy P40’s that there appear to be one or two , what I would describe as 15 or 20mm washers , which seem to protrude from spanwise seams in the upper surface of the wing , at about mid cord . About half of the “washer” sticks up . I imagine these possibly are a form of trim control . Can someone with the knowhow explain please ?