The "clutch" involves multiple parts, as shown here.
The two rings with internal threads shown in the upper left and lower center are used on microphone stands but are not present on guitar legs. They are not relevant to this discussion.
The collar is the big piece with internal threads that turns, shown top right in this photo. The clutch split ring (shown lower right) and the solid unthreaded clutch ring washer (shown lower left) fit inside the collar and slide over the inner tubing. The collar and solid ring washer squeeze the split ring, causing it to expand inside the outer tube as the collar is tightened, gripping the smaller tube in place within the larger.
Hope this is helpful
