Here is the only 'academic' piece where this is discussed experimentally:
http://linkinghub.elsevier.com/retrieve/pii/S0022346803005086
Temporary stretch of the testicular pedicle may damage the vas deferens and the testis
Journal of Pediatric Surgery, Volume 38, Issue 10, Pages 1530-1533
They don't say the displacement though, only the 'force'. However 125g for a 250g rat seems a bit much.
T,
I have been 'stretching' since 2002 and have learned a lot in this time. First, it will work, but you need to be patient, dedicated and listen to your body. Start with a light weight and move on over time to adding more weights. If you want more details, drop me a line, but I am happy to help others get into this...
Hello.
There are various methods for scrotum stretching, including a weighted leather "bull" bag worn around the testicles, leather straps to keep the scrotum from drawing up, steel rings and collars, vacuum pumping, or saline infusion into the scrotum to stretches the skin. Most of the these items can be found in leather stores. I would assume the ball bearings would provide extra weight.
Unfortunately, there is no perfect device readily available, and the implements which are available, even at a high price, are very expensive. Realize also that this must be done very slowly and gradually in order to avoid injury or trauma. Using too much weight too quickly, or even just handling weights roughly or carelessly can cause trauma. Trauma-associated injuries include broken blood vessels, bruises, and the like; however, permanent damage can also be done. So do be careful! For more information, see this site:
http://wiki.bmezine.com/index.php/Scrotal_Stretching