I received an extra bolt in my UC500-XL installation hardware. It is 3-1/2" long, has a lock nut on it, and a 1/2" sleeve. It is not shown in the manual, where does this bolt go?

The bolt can be used if the you do NOT want to use the hitch pin on the hitch receiver. You have the option of using the hitch pin OR the pinch bolt. This is a semi-permanent way of securing the carrier hitch tube to the hitch receiver. There is a 2nd hole on the hitch tube where this bolt would fit. This bolt adds more stability than the hitch pin, but the down side is that it requires tools to remove. 
 

Find the UC500-XL Hitch Mobile Carrier Hardware Parts Breakdown below:

1. Carrier Rack QTY x1 2. Ramp QTY x1 3. Hitch Tube QTY x1 4. Main Tube QTY x2 5. Ainti-Tilt Bracket QTY x1 6. Ramp Bracket QTY x1 7. Spring Pull Pin QTY x3 8. Reflector QTY x2 9. O-Ring Pin QTY x4 10. "R" Pin QTY x4  11. Luck Nut M12 QTY x4 12. Washer M12 QTY x4 13. Bolt M12x60 QTY x2 14. Nut M10 QTY x4 15. Bolt M10x30 QTY x4 16. Bolt M10x40 QTY x2 17. Bolt M10x50 QTY x2 18. Bolt M14x30 QTY x4 19. Nut M14 QTY x4 20. Bolt M18x16 QTY x2 21. Lock Nut M8 QTY x2 22. Bolt M12x30 QTY x2