HEY TOM THAT IS A DUST SEAL BRASS COLORED AND SORT OF T SHAPED THAT GOES ON LAST AND IS ON THE BACK SIDE OF THE KNUCKLE, IT KEEPS OUT THE BIG JUNK ,BUT THE SEAL SHOULD STAY IN PLACE , I HAVE SEEN A LOT OF THE KNUCKLES WHERE THEY HAVE BEEN LEFT OUT FROM BRAKE SHOPS LEAVING THEM OUT I SUPPOSSE , NEVER SEEMED TO HURT ANYTHING ,I WOULD GET THE SHIELDS AND THE NEXT TIME YOU HAVE IT APART ,THEN YOU CAN PUT THEM BACK IN JERRY