Bargman trailer locks made in the 1960s and earlier often used these Hurd H5 keys.   The old L-54, L-55, L-66 and L-77 locks all used these keys.  Be careful because later L-66 locks did not use these keys.  You can tell because of the general shape of the key which has one side with no groove.  Call us for more information on determining whether your old lock might use these keys.  Price is for one key blank.