90% remington 870 bayonet adapter worth

[straightshooter47]

I have had this item ratteling around in my Remington 870 spare parts box for the last 35 years...always thought it was just a magazine extension clamp/support on steriods that Remington offered for the then "POLICE ONLY" 2 and 3 shot magazine extensions. it is brand new with traces of the original packing oil still present. anyone know what it might be worth? would anyone want it configured the way it is without the bayonet lug/sling swivel?

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thanks in advance for any assistance