This is a pair of Hardin Marine 3-1/2" exhaust silencers.
They appear to be new.
They are 3-1/2" outside diameter so they will take a 3-1/2" inside diameter hose.
They measure 11-3/8" overall length and the center silencer body is 4" outside diameter.
They sell for $120 new each, I'm asking $150 for the pair.