Mystery 2x14 grey brick - cannot find instructions with this piece mentioned I have a bunch of LEGO bricks from the years 1975 - 2016. There are a lot of obscure pieces in my collection, but this piece is so obscure that I have no idea what it goes to. If anyone can help it would be much appreciated.
This is item no 812


Train Level Crossing Center Rail Cap Insert 
2 x 14 x 2/3


made for item no 813, the railroad crossing. 



(source: bricklink)

It replaces the 12V straight insert (i.e. it closes the middle gap) when using a 4.5V train system.