The JayCee Broached Pulley Nut with 6061 Anodized Billet Hat & Heavy Duty Washer. Nut comes broached for a 3/8 in. ratchet to make installation or removal a breeze. The head has a reverse thread that the hat screws on, so while your engine is running the hat will not spin off. The billet aluminum anodized hat has a 5/32 in. Allen broach in the center to make installation or removal also a snap! The O-ring seal eliminates vibration & scratching of your pulley. The broached Pulley Nut comes with a Black Oxide finish and the hat (cover) is made from Billet aluminum and then Anodized.