I build this dimensionally identical (internally) to Shaun Wainford's probe
plans.
I cut the top/housing/ring out of a 2" Delrin rod, and the hub out of HDPE using my home-built
"7th Sojourn" dremel-based router.
The pictures show a dart tip that I was using for testing but the digitized dime at the bottom of this post was acquired with a sharpened 2" long 6-32 screw tapped into the hub of the probe. As you can see from the images, the housing of the probe was modified to fit into the dremel mount. It's not as sexy as the probes you guys make out of aluminum but it works for me.
Dime was digitized at .005" between points using Mach3 Wizard and then rendered in Rhino4.