EVERY Ruger Mark IV Mfg. before June 1, 2017 is subject to this recall. Below is a link to a PDF describing the issue and another link to the recall website:
PDF:
http://ruger-hosted.s3.amazonaws.com/email/MarkIV-Recall-Bf28Cz9s46H8.pdf
Website:
https://ruger.com/dataProcess/markIVRecall/index.php?r=y