Thank you for contacting Progress Mfg
One way to determine the size of your hitch is to check on the stickers that are stuck to your arms. If those stickers have faded. Another easy way to determine the size and the rating of your hitch is to measure the diameter of your spring arms, if the arm is 1" wide it would be the 400/4,000lb if the arm is 1 1/4" it is the 600/6,000lb, 1 3/8" it's 1000/10,000lb, 1 1/2" it's the 1200/12,000lb. also if it is 1 1/2" it could be our 1400/14,000lb hitch the way to tell the difference is to measure the C channel or some people like to call it a U channel, it is the part that is welded to the head that bolts the head of the hitch to the shank if it is 3/8" wide it would be the 1200/12,000 but if it is a 1/2" wide it is the 1400/14,000. I hope that this is helpful in determining the size of your hitch. If you have any further questions or concerns please feel free to contact us
Have a great day!
533 South 500 West
Provo, Utah 84601