Bolt on type machined from 2024-T3 aluminum with gold or black colored chemical coating to air in corrosion resistance. The AX5 bolt hole spacing: 1-3/8 x 1-3/8. The AX6 bolt hole spacing 2 x 1-1/8. Use castle nuts MS21025-20 for 500×5 or MS21025-24 for 600 x 6. Spacers are also available A484, A484-4375 or AS200-110.