Brick or set ID for part? Going through 130 lbs. of 5 decades worth of parts and can't ID this one part.  Anyone know what it is or where it's from? It appears to be old light gray but may just be really dirty light bley. It is 2x2x1-1/3 tall. Could be missing it's bottom as it doesn't place on studs. Only number on it is 4.
That's a Technic Engine Piston Square 2 x 2 - Old.