1515-1 rubber bumper is used on the Burr King 150/200 in two locations. 

The 1515-1 (5) are used below the vibratory bowl and help isolate energy to the bowl.  Over time the bumper will harden and may become brittle. 

The 1515-1 (4) is also used as feet on the vibratory bowl. 

It is recommended to replace all rubber bumpers if they are degraded.