Ergonomic Grip for Needle Collet v2

More ergonomic grip for the standard needle collets commonly used in microscopy (see photo). In the .scad file you can adjust the bore to account for tolerances (original holder is 5 mm in diameter). In the provided .stl this is set to 5.5 mm, which works well for me with PLA. It takes a bit of force to push in the metal grip, but still allows removal.
Minor changes from the original design: now all hollow, slightly improved printability and cooler endcap.