5% is not a measurement of absolute stretched length of a penis. It means the connective tissue much be stretched to 105% (an additional 5%) its length AFTER FULLY UNCRIMPED.
So you can better understand this uncrimping thing, let me give a brief explanation of how the collagen composing most connective tissue works. Collagen is an amazing molecule with several properties that make it an ideal candidate for use in connective tissue: it is elastic but also has viscoelastic properties allowing it to stretch further and dissipate energy more efficiently under loads without snapping, it can form polymer chains allowing it to be structured into connective tissue of any size, it forms cross-bonds with adjacent collagen molecules making the connective tissue much stronger as a whole, and, important to this discussion, when collagen forms polymers, these polymers like to fold up on themselves when not stretched, like an accordion. This is what is referred to as “crimping.”
When you apply a load to connective tissue the crimps unfold before the collagen actually begins to stretch in earnest. This is why it is hard to say just how far of a stretch 5% actually is in terms of the stretched length of your penis. You do not know how much of any given stretched length is due to uncrimping or how much is due to deformation.
I would suggest using progressive, measurable gains in stretched length as an indication that you are achieving 5% deformation or slightly more. If you are gaining then you know approximately the “feel” of a stretch that is overcoming your threshold for permanent deformation. When those gains start stalling you can be reasonably sure deformation is no longer adequate. Note, you do not want to apply loads that are sufficiently large as to produce deformation of well over 5% for long periods of time because your connective tissue will have a tendency to increase in toughness by a lot to protect itself making progress more of a challenge.
@Wawawuh: how would you be hanging? If you are hanging light, like 5-6 pounds max, then the lighter springs would be OK and compliment the hanging nicely. Although I’ve never seen extender springs which produce over six pounds of force so the heavy springs should work as well, perhaps better in the long run.
Now, if you are following the hanging guides on this site/Bib’s site then you will be working up in weight incrementally over time and eventually - rather quickly, in fact - be hanging some heavy weights. Because your penile connective tissues will constantly be adjusting to the load as it is increased an extender, even one with upgraded springs, would quickly become ineffective as the tissues of the penis toughened because the extender would lose the ability to produce an adequate force to pull the now toughened penis into a long enough stretch to breach the threshold for permanent/plastic deformation.