The Mizuno 921 Forged irons compared to Mizuno 919 Forged irons have stronger lofts with faster ball speeds. The Mizuno 921 Forged irons are the first time Mizuno has incorporated Chromoly into its forging process, resulting in a stronger material. , The difference between the Mizuno JPX 919 and 921 is very simple. The 919's are the version from 2019 that is now considered the "older model" meanwhile the 921's are the 2021 model which had increased forgiveness and better feel than the 919 model. Therefore, overall the 921's are an upgraded version of the 919. , Mizuno 919 and 921 are iron sets from different years. The 919 is from 2019 and the 921 is from Mizuno's 2021 irons line. The JPX 921 SEL iron set stands for "Special Edition Lefty".