So, I finally found out what the heck the specialized dremel bit is called that I've been using for the last 14 years. It's a 1 1/2" long, 1/8th diameter 'center cutting 4-flute single end mill'. It's the most useful bit in my toolbox. It has a bladed end so you can drill straight down into plastic with it, just like a drill bit. The edges aren't spiraled like an ordinary drill bit but instead are straight. This means it won't continue pulling or drag across a surface. And unlike an ordinary drill bit you can cut sideways with it and not have to fear it breaking. NEVER try that with a drill bit. You can also widen holes, precisely shave plastic, completely grind off the surface of something, cut through an action figure limb, and drill a perfectly cylindrical hole for a peg, screw, post, or round magnet. You can create V-shaped battle scarring/gouges by tilting this bit on its edge and I haven't found any other bit that can do that.
You can google to find a tool shop that has them but they usually run $20 and then a whopping $11 shipping on top of that for a tiny little bit because they all use UPS. I'm buying a whole bunch in bulk so I can get a discount and pay just the one shipping cost. So if anyone wants one email me and I'll be happy to give the details. But however you get a hold of one, do so, because it will make things so much easier to customize.
Here's what you're looking for.