Help identify this engine part please (see pictures)

I was wondering what this was, I thought it might be the oil drain plug but it's not on the same side as the filter.
The tractor is a John Deere 335 with the 20 hp Kawasaki air cooled engine. Thanks,

Attached Images

• DSC09553.JPG (136.0 KB)
• DSC09552.JPG (137.1 KB)
• DSC09550.JPG (132.8 KB)