This Ash Cup twists onto the air channel support located at the very bottom of the pellet grill. The ash cup collects the ash from burned pellets that falls through the firepot bottom holes. This helps your pellet grill burn better by not building up in the burnpot, not to mention it makes it a lot easier to clean out that part. You should clean out the ash cup before each use.
In the manual for the Oklahoma Joe’s Rider DLX Pellet Grill 900 and 1200 models this is listed in the parts key as item #54.