336 rc

I was taking apart a 1950 336RC, removing the magazine tube and I heard something hit the floor. I later found this small piece. Anyone know what it is and where it goes. I do not see it on a schematic.

Greetings! I've just acquired a Marlin 336RC in 30-30, and I need to give it a thorough cleaning. I've found instructions on how to "field strip" it for cleaning -- but it has mild rust spotting all over, and I am wanting to address that, and re-blue. I found the user manual on the Marlin...

I just ran across a beat up 336RC, and the Stock is cracked pretty bad. I would like to stay as original as possible, but a synthetic will be an acceptable last resort. If anyone can point me in the right direction, I would greatly appreciate it. Thanks in Advance, Geoff