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Yep-- they’re metric, not SAE. Most of them are 1.5mm & 2mm, with the really tiny ones at 1mm. If your local big-box hardware store doesn’t have a set with the smaller sizes, check a local RC hobby shop or (much cheaper): http://smile.amazon.com/dp/B00I5TH074 3
Cheers, Dennis
Ultimaker along with most 3d printer manufacturers use metric with printers so you’ve likely bought imperial sizes.
I think it is very likely that you purchased SAE Allen wrenches rather than metric Allen wrenches. If you get the metric ones you should have no more problems. Please let me know if you have anymore questions
Wow guys, thanks for such great response! we actually bought them in Amsterdam so its pretty silly that they don’t have something fitting. The one I have here seems to fit well, but its like a tiny bit too loose… I am afraid that the part itself might be worn out or something 
Most of the nuts and bolds that are bought by machinebuilders etc… come from companies that buy their products in low cost countries. They do meet the requirements of 8.8 or 12.9 bolts. But quality is evryting but… eccentricity, and damaging of the inner hex is very easy (even within torque specs) , witch prevents good tightening. So good chance is that your inner hexes are damaged. For my UM2 I encountered this a lot! BTW, every techician should have a pair of these! http://www.pbswisstools.com/nl/quality-hand-tools-qht/color-code/rainbow/inbussleutels.html
The vast majority of the screws on the UM2 (and the UMO) are 2mm hex. A ball-headed hex driver is useful for working on some of the harder-to-reach screws, especially the set screws in the pulleys.
On the UM2, you’ll need a 1.5mm hex driver for the set screw on the feeder knurled sleeve and the 14mm set screw that holds the temp sensor and heater into the nozzle (the one indicated in the followup picture). A 2.5mm hex driver is needed for the z-stage bearings under the cover in the back of the print table.
For people looking for something a bit better than the Allen keys that come with the machine, fbrc8.com (my company) sells a complete toolkit of the same high-quality tools that we use in assembling the UM2. You can find it on our website.
They are 2mm allen wrenches. I strongly recommend you get a 2mm hex wrench in a screwdriver package (not those L shaped ones although it’s okay to get one of those also). That covers 99% of the screws on the machine. There is a single screw in the heater block that is 1.5mm and the fans may or may not have phillips head screws.
Hey guys,
We’ve tried everything! Thanks for all the help! We even tried soldering the tool to make it little bigger and then gradually reduce the size of it, but it was still either too big to fit or simply spinning inside.
We called the Ultimaker and they’ll send us the original tools, but I don’t think that will help. We’ll see if can work it our over e-mail with them as well. It seems like the only thing we can do now is change the whole nozzle
Just take vice grips and squeeze the hell out of that little screw and rotate it out.