This is now available in my Etsy store, along with a larger version covering larger screws: https://cmhprinteddesigns.etsy.com/

TL;DR: There are currently four versions of this thing available for download:

• Metric screw measuring device.stl
  Original remix of Sneak's awesome original.
• Metric screw measuring device - sanitized.stl
  If there's one thing Thingiverse folks hate it's someone else's name on something they print. By popular request, I removed the names from the back. God forbid someone wants credit for the thing they shared with you for free!
• Metric screw measuring device - with threads.stl
  Inspired by some of the great remixes of this design, I added printed-in threads to the back. Requires printing at a finer layer height to maintain the precision of the threads, or cleaning up with taps after printing.
• Metric screw measuring device - thread markings.stl
  Same as above, but with the thread spec printed into the back next to each hole.

NOTE: This is a re-upload of thing 4154091 which was quite popular (almost 10k likes) and featured on the front page. I made a small update to it, adding the model with the included screw threads in the back, and ever since that update the thing is still there but returns a 404 error for everyone who isn't me. I've tried to get it to post, I contacted thingiverse who never responded, and have finally decided to try and try a completely fresh upload.

Update 8 Dec 2020 - I previously uploaded the version with threads printed into the back (silver version in the photos) and have been using that, but I got contacted by K_tech asking which threads I had used. While I was able to answer the question, I realized that I had missed an opportunity to label the threads on the back. I have now uploaded a new version (white with black lettering in the photos) which has the threads marked in the back. All of the previous versions remain for downloading.

Update 20 Aug 2020 - I'm a big fan of m750's remix because it has nuts press-fit in the back, and I have some SAE screws that get in amongst all my metric stuff, so I like to confirm if there's any question. I have printed several of that one, but realized that I wanted to have threads in my design as well. There's just enough room in the back - maybe not for press-fit nuts, but I can do printed-in threads. I've printed off the new one (see the silver print in the photos) and it works well. I did chase all of the threads with my metric tap set, but they didn't require too much cleanup after printing at 0.2mm. The originals without the threaded holes are still there as well.

Update 28 Feb 2020: Per a request I have uploaded a version with no keychain loop or back text. This is available under Metric screw measuring device-sanitized.stl in the Thing files.

Other good alternatives:

• sneaks' original design with threaded inserts
  If you have heat-set inserts on hand, Sneak's original design is awesome, and more durable than printed threads.
• m750's remix with nuts as inserts.
  If you don't have heat set inserts on hand - you probably have nuts of the right size. This is one of my favorite remixes (even though it's a completely new design) which covers a range of larger screws. I use this one in my bike shop as the range of sizes covers what you're likely to see on a bicycle better.
• Other remixes
  If you think "this is a good start, but it would be better if..." - odds are someone else thought the same thing and has already posted a remix. There are some great alternative designs which folks posted as a remix of this, definitely check them out.

Note about standard lengths

I've gotten several comments about the ISO standard lengths and how it goes up in 5mm increments past 20mm and so forth, and several requests to redo this with the standard lengths. There are already several remixes which have done exactly that. The problem is not every bolt and screw complies with standards. I have right here an M8x22, an M6x15, and an M4x13. If I had the markings on the "standard" lengths, it would be difficult to determine the exact length of those. Because of this, I have no plans to change Sneak's excellent original design and don't find it that hard to read. If you are certain you'll always deal with bolts which conform to the standards, then check out the remixes.