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Nozzle extension ID plate. It reads

ROCKETDYNE

A Division of North American Aviation Inc.
Name: Nozzle Extension
Spec. No.: WT. 1627.0 lbs.
Mfgr: Precision Sheet Metal Inc.
Part No.: 209210-31
Serial No.: 8355253
Insp.: <Inspector's stamp>

Rocketdyne apparently had at least two vendors for nozzle extensions. While most nozzle extensions that I've seen were manufactured by Precision Sheet Metal Inc., a nozzle extension with an earlier part and serial number was manufactured by Rohr Corp.

This particular nozzle extension incorporates and engineering change wherein the aft hatband has a tubular, rather than rectangular, cross-section. There are only a few F-1 engines on display which exhibit this modification; the two such nozzle extensions for which I know the part number are both 209210-31 (i.e., the "-31" model).