String (or a stronger string-like material such as twine or leather) may serve as a lock for certain less functional tablet cases styles. A string lock provides the user with an easy-to-use fastener that is tied on and taken off very intuitively.

Most commonly seen in envelope cases and sometimes in other styles such as sleeves, a string lock typically consists of the string itself and a pair of circular buckles. The cover of the tablet case is thus anchored shut by wrapping the string around the buckles or in a figure-8 style.

Naturally, the potential weaknesses of the string fastener are easily figured out. It is imperative for the prospective owner of a tablet case with string lock to check the anchoring buckles. If these are not well-stitched and/or properly riveted onto the exterior, the given case simply will not fulfill its function for long. As for the string itself, twine and leather are clearly more appealing and heartier than standard thin string.