M4 grub cap. There is an indentation on the side of the hopper throat to allow space for a screw head to fit, with the threads going through into this part. Fiorenzato #400000096. The screw only is G_631.
WARNING: This product can expose you to chemicals including lead, which are known to the State of California to cause cancer, birth defects, or other reproductive harm. For more information, go to www.p65warnings.ca.gov.