I did a careful bench test of my X4 Labs, and I found
1. compressed down to 1 ring exposed takes 6.3 lbs. (2957g). This is a loading almost but not quite complete bottoming out so the springs are still holding the test weight.
2. compressed down to 2 rings exposed takes 4.6 lbs (2188g)
3. compressed down to 3 rings exposed takes 2.6 lbs. (1240g)
I have read the rings are supposed to be something like 600 grams, 1200 g and 1500g- not what I found at all. Either the ratings are for only ONE spring and you are supposed to double it, or the ratings are simply advertising bullhockey. I suspect they are full of bull but since I did not manufacture them I could not say. I only know that my test found the penis extender is far stronger than that. My test used water loading, and I accounted for tare of the system. Friction was hard to estimate but I took several readings to get an average. Since the weight of water is known, I measured the amount of water it took to reach a certain position on the extender which was the 3 rings. It was a pretty accurate method, +/- about a quarter of an ounce for water meniscus error plus something for the tare error, but no more than around an ounce total which equals +/-28 grams.