This is a rail anchor. The rail anchor measures 1" (h) x 8.25" (w) x 4" (l).
According to museum volunteer Tom Peyton, this anchor is mounted on the inside of the rail next to a tie.
Lexicon
Nomenclature 4.0
Nomenclature Primary Object Term
Component, Track
Nomenclature Sub-Class
Rail Transportation Accessories
Nomenclature Class
Rail Transportation Equipment
Nomenclature Category
Category 07: Distribution & Transportation Objects