Line rail. Railway rail.

The rail nail (usually referred to as a track nail, rail spike, or railroad spike) is an element used primarily in Palo Mayombe witchcraft and strong magic practices within Afro-Caribbean contexts to bind, pin, protect, or separate energies. 

• Binding and Fixing: Due to its original function of securing train rails, it is used to "pin" a person, situation, or energy so that it does not move from where the practitioner desires.
• Protection: It can be used to create energy barriers, keeping witchcraft or negative energies away, serving to "lock" a place against harm.
• Separation/Dominion Magic: It is used to separate two people or to dominate someone's will, preventing their free action.
• Rayamiento: In Palo Mayombe, the use of strong iron elements is associated with the pact with the dead and the firmness of the "prenda" or cauldron.