The end cap will have to be removed to get this measurement (
see video for more information at 7:00 minutes). This is
a measurement from the sling rail’s top edge to the lower edge of the sleeve (the
sleeve holds the spline cording). NOTE: Typically, 0.31 (5/16”) is standard. Measure
only one side, do not add the opposite side.
If your chair contains two different sleeve sizes (which is uncommon), add the two
sides together and divide that total by 2 and enter the result.