It is a chromoly steel flywheel, works perfect for my combination for street and track. Here is a link to the spec from Exedy's website:
https://shop.exedyusa.com/exedy-rac...ng-hyper-single-series/eh06sd1/i-2292398.aspx
https://shop.exedyusa.com/exedy-rac...ng-hyper-single-series/eh06sd1/i-2292398.aspx