Ford 260-289-302, 351W, uses 3/8 socket. Black oxide chrome moly with a Hex Head. 3/8 x 16 thread Prevent intake manifold leaks and arerated at 170,000 psi and precision machined for optimum thread engagement. Wide under head flange and companion washers provide even load distribution. ARP Intake Manifold Bolt part number 154-2001Precision rolled threads prevent galling while promoting more consistent torque loading. Facilitates optimum sealing of gasket surfaces Washers are included.