Wilwood's newest Five - bolt drive flange has been redesigned with a sealing boss o - ring to create a leak proof seal. There is no need to use gaskets or sealer to retain differential oil. Our drive flanges continue to have long standing reputation for durability. These five bolt drive flanges are machined from 7075 - T6 alloy. 'L' part numbers are supplied less flange attachments bolts for customers preferring to supply their own attachment hardware.