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. Measures 1-7/8". Call us for more information on determining whether your old lock might use these keys. Price is for one key blank.