This is a Mesa Tactical Stock Adapter known as the Lucy, model 93890.
This cast steel adapter enables the use of any 12 gauge Remington 870 stock. There are many more options for the 12 gauge than 20 gauge" including Mesa Tactical's Urbino Stocks" telescoping stock adapter kits and even the Hydraulic Buffer system.
Features:
Stock Adapter
Allows 12 Gauge Stocks to be used on 20 Gauge
Fits Remington 870
