It does not appear to be a Model A part to me. Round Model A step plates had a square hole in their center and were mounted with a carriage bolt down through the center. Possibly later Ford part.
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Jim
'29 Ford Model A Phaeton (MARC #71406)
'63 Riviera, Fawn Mist, Saddle Leather (ROA #9774)
Jim's 1963 Riviera