Finned style secondary will not fit under stock housing and modifications to the clutch housing would be required to use a stock housing that is suggested. This is an all billet construction and capable of using compression springs with different spring rate options available. We have many helix angles see menu for available options. We can also provide custom helix angles if you desire for an additional fee. Comes with bolt for installation. Can be used along with the stock primary or the STM primary. Best results are acquired when running both the STM primary and STM tuner together..