well I've been using the standard back springs that came from the manufacturer,(tattoome) which I've replaced, only to find they snap a week or two later. however in yesterdays case it snapped the very next day on a new machine. i adjusted the contact screws when using the t tech parts, and dropped the volts slightly, as my machines are build to run between 5-7v. so the machines tuned as far as i could tell, and puts in a lovely solid line no problem, no issues when tattooing, until the breaks. .. i can't help but feel it is a case of finding some thicker back springs, so far I've been replacing them with the same spring set. ill order some different springs and see how that works out.