The MTA Monday said the broken rail that caused the derailment on Friday replaced a rail where a crack was discovered.

A specialized rail car that checks track alignment every three months spotted the hairline crack at the location where the train derailed, the MTA said. That crack prompted the installation of the rail that ultimately broke on Friday morning near the 65th Street station in Queens, causing six cars on the F train to derail, injuring 19 people.

The U.S.-manufactured rail from longtime supplier ArcelorMittal that is being analyzed by a metallurgist was shipped to the agency in December and installed in February, according to the MTA.

"The MTA is in the process of locating and inspecting other rails from that batch," the agency said in a statement.

The Queens Boulevard lines were identified as having among the highest rail breaks in the system, with 205 breaks between 2005 and 2012, according to MTA documents. In the next capital program, the corridor is a candidate for getting a new type of rail that has long sections welded together, providing a lower rate of breaks per mile and a longer track life, according to the documents.