I designed these knobs as replacements for my Unication G5 pager.  You'll need the D-rings that go around the knobs to fit in these.  The center pin for the middle knob prints separately.  Because of its size, you'll need to trim the base away from it.  The pin then gets inserted into the hole in the middle knob.  I have found that reaming the top of the hole out slightly helps clear extra material that may have prevented the hole from becoming round and allows the pin to move more easily.