This model features a vise grip with adjustable jaws. The model has various joints, a flexible spring element and a thread to adjust the width of the jaws. 

The model can be printed without any supports or manual assembly/post processing. Clearances between moving parts are 0.3 mm.

Update V1.2: Optimized thread geometry to prevent slipping at low infill/wall line print & optimized spring element geometry

Update V1.1: I limited the maximum movement of the release lever to avoid damaging of the flexible element