Oil fill hub cap for bolt-on wheel end installation on commercial truck and trailer axle applications Aluminum and metal construction for lightweight durability and corrosion resistance at the wheel end Bolt circle at 4.50" with 6 bolt holes for secure, repeatable bolt-on mounting to standard hub faces Oil bath lubrication type with fill plug for service-friendly oil level access during maintenance intervals Height at 2.61" for correct axial clearance in wheel end hub cap positions on standard truck axles Oil-level inspection feature for at-a-glance lubrication monitoring without full hub cap removal