What is referred to by 'arm nut'?

What is associated with: arlington national cemetery which is home to the mast of this ship that blew up in 1898? Based on the clue 'arlo guthrie im the train they call the city of th...', what is the answer? Based on the clue 'arlo guthrie starred in this 69 film inspired by h...', what is the answer? What is referred to by 'arm bone ln'? Based on the clue 'arm of al anon thats specifically for young people...', what is the answer? Based on the clue 'armadillo teeth dont have this the hardest substan...', what is the answer? Based on the clue 'armageddons tyler weds spartacus author howard ta...', what is the answer? What is referred to by 'armagh down londonderry'?