Like my 5in revision this has some more material (and strength) to the joint between cylinder and arm. I've also added more material to the prop holes so that standard M5 & M3 screws fit without using a nut.
The most important change is the multiple sizes available; 3, 3.5, 4, 4.5, 5, 5.5 and 6 in.
Updated version (160309) is 5.5mm higher so more dremel tools can be used.
Shapeways (3-7in): https://www.shapeways.com/product/NY7GF4PAG