Typically, locating pins are used for controlled, fine tolerance positioning of a work piece.
For example, a pallet that is moved along one axis, where the drive mechanism is not accurate and stable enough to place it in a position sufficiently accurate to execute a particular process, the use of locating pins may be the best solution.
Usually two locating pins are enough to properly locate the work piece on one plane.
The Diamond Shape is a critical feature that helps with machining inaccuracies and smoother locating operation.
When two round head pins are installed onto one plate, the distance between two mounting holes must be extremely precise and even then, the work piece will not be placed on the base as easily as it would with the use of a diamond shape pin.