* The wheels themselves: The bolt pattern (e.g., 5x5.5", 6x5.5", etc.) is usually stamped on the back of the wheel.
* Your owner's manual: This should specify the bolt pattern for the factory wheels.
* Your vehicle's title or registration: Sometimes the wheel information is included.
* A Ford parts website: Using your VIN (Vehicle Identification Number), you can look up the specifications for your truck.
Most commonly, 1988 F-150s used a 5 on 5.5 inch (5x139.7mm) bolt pattern, but it's crucial to verify this with one of the methods above. Using the wrong bolt pattern can be extremely dangerous.