Forward assists and dust covers are two main parts that normally don’t come with your “stripped” upper receiver when purchased. These two parts are common for anyone that is building an AR-15 to have to add to their new upper. The forward assist is something that allows you to hit with your hand in case your bolt locks up when in the field, while the dust cover can be used to keep debris from entering the firing control unit on your AR-15 when not in use.