Antique Vintage Rusty Farm Equipment Gear

I found this on an old family farm in 2008 and was informed it was likely from the 1940s-1950s. I thought it was cool so I took it home and wrote in sharpie on the back where I got it. I vet that would grind off very easily. It's super Rusty, so don't handle with open cuts. it's about 5"-6" diameter