This product alone could not open my old, stubborn screw down case backs. It could not hold the friction needed to loosen it.

As a supplement, however, this ball is great. I ended up getting the&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/SE-Watch-Opener-Spanner/dp/B000RB0GOW/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">SE Watch Opener Spanner</a>&nbsp;and that opened the case back without a problem. I now use the spanner to loosen a closed caseback and the ball to twist it all the way open. then to close, I reverse the order. Ending with the spanner to lock it up tight.