Proflow Cylinder Head, Ford Thermactor Port, Threaded Insert, Accessory Bush, 5/8-11 od To 7/16-14 id, Steel, Black Oxide, Set of 4

Proflow Small Block Ford Thermactor Inserts These small block Ford thermactor inserts are designed to thread into your heads to change the thread size. These inserts thread right into the existing cylinder head thermsctor ports to allow use of the factory accessory drive bolts. Also required for many aftermarket cylinder heads to reduce from 5/8 thread down to 7/16 for mounting factory accessories, eg:AFR-1422