can using those "gripper" things cause carpal tunnel? I mean the spring things that are two dowels connected by a spring that you squeeze.

 From what I heard, those grip things put to much stress on your tendons, because they are getting squished.  Using them too much swells up your tendons, thus forcing the nerve in your hand to get squeezed.
 Some people say that you should only squeeze half-way, if you do it frequently.  If you rarely use it anyway, then you could squeeze all the way.
 A better alternative to increase grip strength is doing wrist curls, or hammer curls.


Hope this helps.

After reloading constantly for the past 10+ years, my hands are shot.  Whenever I load up a big lot of 5.56 and 9mm (several thousand each), my hands are numb for a month.

Usually, Repetitive Stress Distorders (RSD) are caused by significant repetitions of the exact same movement, usually with lightweight stuff.  The heavier stuff happens much less frequently.

I used to run operations at Frito-Lay's biggest plant, and most of the labor consisted of picking up bags of chips and putting them in boxes.  Our CTD/RSD illness (not injuries) made up about 30% of the employees.  Mucho dinero in off-time, doctors, modified duty and slackers.

If you're just trying to get some grip strength, but not doing it constantly, every day, it probably won't effect you.