This is the tang screw (stock screw) Winchester 1906 EXPERT and the very rare 1890 pistol grip pump THAT IS USED TO ATTACH A TANG SIGHT. The screw goes through the back of the tang sight hole and down through the stock holding both onto the receiver. If you do not know if you have the 1906 EXPERT, take a look at the upper and lower tangs on you trigger guard. (the two pieces of metal that extForearm back from behind the hammer and trigger that fit into your stock) If the bottom tang curves downward and away from the upper tang to follow the downward curve of the stock, then you have a pistol grip.
