Here what Klein Customer Service said:
begin quote
The most recent issue of the Tradesman club suggested working WD-40 and
kitchen cleanser into the pivot joint to loosen them up. They way they
adjust them in the plant is with a hammer and anvil. If you place the
rivet over a hole in the anvil (about the size of a quarter) and strike the
other side of rivet lightly with a hammer, it should loosen. Be sure to
wear appropriate safety equipment, etc.
end quote