Railroad ties are rectangular pieces of wood with specified dimensions that are used to hold steel rails apart by a fixed distance in track. They’re dried, treated with a wood preservative and installed in track with various types of hardware to support the load and to keep the wood from being crushed and worn away during service. Specifications for ties vary slightly from one customer to another.
Conners, Terry, "How to Select and Buck Logs for Railroad Ties" (2016). Agriculture and Natural Resources Publications. Paper 98.