This is a Butler Creek folding stock for the Mossberg 500/590 series. It is the most solid folder out there. Includes all necessary hardware to convert your m500 into a folding stock gun. Also includes a [b]bonus polymer forend[/b] to make a complete "black shotgun". The buttstock is also easily removed to produce a pistol-gripped shotgun.
These go for $100 online; I'm asking $70 shipped.
Thanks for looking!