Back in the 70s I went to Stores in Valley to sign out my ejection seat leg restraints.
"Sorry" I was told, "We only have one left in stock".
"Thats OK. I'll come back when you have some more".
"No. You have to sign out the one leg restraint because we can't order a new box until the current stock has gone".
And so I spent a week with just one leg restraint (fortunately during the Ground School phase although I had to borrow a leg restraint for my Hawk famil ride). It transpired that they came in boxes of seven.