Part Number	Location on Vehicle	Spring Capacity	Number of Leaves
43-1289HD	Rear	8,000lbs	10

This is an HD (Heavy Duty) version of the original spring. It's heavier than what was originally offered on these trucks from Ford. 

Part Number	Location on Vehicle	Spring Capacity	Number of Leaves
43-1747	Rear	5,500lbs	10

Part Number	Location on Vehicle	Spring Capacity	Number of Leaves
43-1289	Rear	5,900lbs	10

This is the original version of this spring and there is also an HD (Heavy Duty) version available.

Part Number	Location on Vehicle	Spring Capacity	Number of Leaves
43-1747HD	Rear	5,500lbs	10

This is a Heavy Duty upgrade for the stock springs.