This is the CaliBlock (calibration + block). It's a calibration print that can be also used as a nifty building toy. If your printer is reasonably well-calibrated, CaliBlocks will snap together much like Legos. No pins or screws required.

TAKE THE 1 HOUR CALIBLOCK CHALLENGE! Try to print a "caliblock normal half" in less than one hour. It's a challenge for most printers! You must meet the following conditions:

• Be honest! Nobody likes cheaters.
• Actual recorded print time must be less than 1 hour, slicer estimates don't count.
• No scaling, final dimensions must be +/-1% of the targets.
• 1-hour CaliBlocks must clip and unclip with other CaliBlock without breaking.
• Post a close-up "make" photo of the print along with your printer model and slicer settings to prove you did it.
  If you succeed, you get a million 3D printer points!

Version history:
Rev 5: initial upload
Rev 6: Beveled corners on clips to make it less sharp on hands
Rev 7: Beveled some corners at the base of half blocks to further reduce sharpness
Rev 7b: Added "tight fit" option to reduce play for people with super-precise printers (from 0.3mm per clip to 0.1mm per clip)

This was inspired by the 3D Benchy boat (http://www.thingiverse.com/thing:763622). Calibration prints should be fun! This print is great for:

• Overhangs... it's chockablock full of 'em. But all overhangs are less than 60 degrees so it's completely printable without support!
• Retraction... there are SO many retractions. SO MANY.
• Print strength... if the clips snap off, your print is too weak! The model geometry is specifically oriented to maximize clip strength.
• Dimension tolerance... the clips should be a snug snap-fit but also removable and reusable. If you're crazy over-extruding, it won't go together. Also, the square faces are 20x20mm with a 12x12mm hole and the edge-to-edge length is 60mm,
• Ringing and position registration... it's got tons of great sharp turns to shake your printer!

I strongly recommend printing two "halves" and gluing them together. No support required. But if you want to work on supports too, go ahead and try to print the "whole" model in one go. It should be good for testing dissolvable filaments and different slicer support types.

Note: I came up with the idea independently, but I want to give credit to the BUBO block for beating me to the punch with a very similar toy shape: http://www.thingiverse.com/thing:685490