Rach,
That was probably the screw that holds the stud in. Those studs can get stuck by age and dried up oil. So give it a good soak in denatured alcohol then gently work it.
I don't know what kind of rotating knob that tension has, but if you put the knob back on the stud you can then stick a screw driver through the gap under the know and gently try to turn it.
Joe