Hidden mount screws; billet 7075-T651 aluminum and exact positioning to the centerline of the cam bushing and pinion bushing within .0002". Features improved breathing; which is good for stock and even better for high performance applications. A positive two O-ring seal systems will keep oil where it belongs. These JIMS 2-piece gear covers are among the best made. Note: For replacement o-rings see 978025 (small) and 978026 (large).