This is a standard steel floor plate from a pre-war Winchester Model 70 rifle. It has rust-bluing, which was used on bottom metal up until 1939.
Bluing - 90% - The finish shows mild edge wear. There are some small inconsistencies in the bluing and a few light scratches.
Metal - A few light scratches, otherwise no pitting or other defects in the metal.
We use the NRA Modern Gun Condition Standards Grading System for grading part conditions. You can read about it HERE