Get rid of your course threaded optical sensor that is a royal PITA to set. This takes a little work but is worth it!

First you need a few things.
I used the small micrometer from this set at harbor freight:
http://www.harborfreight.com/3-piece-micrometer-set-66512.html
I also ordered these micro switches part number ES3RL:
http://www.amazon.com/Endstop-Microswitches-3D-Printer-CNC/dp/B00G2E6UZC/ref=sr_1_1?s=industrial&ie=UTF8&qid=1408573041&sr=1-1&keywords=endstop+microswitch

First, you have to saw off the "C" portion of the micrometer. This will leave just the threaded handle and shaft. Next print both files. Remove your old optical sensor and flag. Cut the old optical sensor from the wire loom. You may need to extend the wires for full bed travel. Solder the white and black wires to the tabs at the ends of the micro switch. The center tab is not used. Mount the microswitch to the "MH3000 microswitch z.stl". Insert the modified micrometer into the "Caliper mount V2.stl". Mount both on the printer so that they line up. Move your bed to Z home then turn the caliper slowly until you hear the microswitch click. Verify your Z home is the correct height from the bed. Enjoy!

Edit:
I added a low profile mount. This allows the bed to travel all the way up to the threaded rods. I had to make the adjustment after I added the Diamond Hotend to my printer.

First, you have to saw off the "C" portion of the micrometer. This will leave just the threaded handle and shaft. Next print both files. Remove your old optical sensor and flag. Cut the old optical sensor from the wire loom. You may need to extend the wires for full bed travel. Solder the white and black wires to the tabs at the ends of the micro switch. The center tab is not used. Mount the microswitch to the "MH3000 microswitch z.stl". Insert the modified micrometer into the "Caliper mount V2.stl". Mount both on the printer so that they line up. Move your bed to Z home then turn the caliper slowly until you hear the microswitch click. Verify your Z home is the correct height from the bed. Enjoy!