This is a pair of adjustable pliers based on a rotating tongue-and-grove mechanism. They are fully functional, and are especially useful in cases when non-marring tools are required.
The form of these pliers, especially in terms of the handle shape and ergonomics, is derived from a very old pair of pliers manufactured by the Diamond Tool and Horseshoe company. However, the adjustment mechanism is of a more modern style, and is identical in principle to modern commercial products available from many manufacturers.
This model may be scaled as needed depending on your needs, and functions well at any size. Since Galaktican reports that the snap ring is a bit tight, it may be advisable to scale this component up by 2-3% relative to the other parts.
Also, thanks to the folks at 3dPrint.com for writing a nice article about this thing! http://3dprint.com/55290/3d-printed-pliers-tools/
All three parts should be printed in the given orientations with no support material. A high infill density is necessary if the pliers are to be used for heavier gripping tasks.