Whatever this part is called, it came off my mower today. It goes on my Exmark Metro's rear wheel. It basically holds the wheel on the axle. There's a groove that goes around the axle and this clip snaps into place and holds it on. My local dealer didn't have any in stock!. I'm just trying to find out what it's proper name is. I've looked in some catalogs I have and it's been referred to by different names. "E" Ring, Snap clip, Retainer ring. Are they all correct, or is there is difference? Just curious for future reference. Off to another dealer now. Hope they have one!