This is a keyring-light that consists of three printed parts, a LED and a battery. The dimensions of the latter two should be: - LED: a diameter of 4.8 mm and a rim at the base with a diameter of 5.4 mm and a width of 1 mm - battery: 2 mm thick and a diameter of 12.3 mm (CR1220) The dimensions are crucial, and I found that they vary with layer height. I printed this with an Ultimaker 2 and sliced the model with Cura with the following settings: - layer height: 0.1 mm - infill: 40% (20% might make top surfaces less smooth, which might not be a problem, but it hardly affects print time) - print speed: 40 mm/s (80 mm/s also works, but doesn't look as good) The three printed parts are: - lower cap - upper cap - slide It should all fit snuggly, for which I used tight fits. So postprocessing is probably required, for which I use a nail file, a course file and a round file that is the diameter of the LED (smaller would of course also work - alternatively, you might use fairly fine grained sandpaper wrapped around a big nail or such). Filing will most likely be needed for: - the outside of the lower cap ring (in which the LED is to be placed), especially the top; this is the top of the print, so there may be some ooze. This would make it difficult to place the upper cap over it. But don't file the protrusion down completely, because it keeps the lower cap in place. - the insides of the lower and upper cap rings. This is where the round file comes in handy. - the sliding parts of the slide and the upper cap. Especially for this a thin nail file would be very handy. An 8 mm wide file would fit nicely in between the slide-bits of the upper cap (I bought mine at a SPAR supermarket). You might finish this off by sliding the parts back and forth a few times to smoothen the surfaces. And possibly also, so the keyrings will fit throught the vertical slots in the slide: - the keyrings-holders - the inside of the keyring-holder holes of the slide The legs of the LED have to be prepared. First, they should be bent outward at the base because they are not far apart enough to fit across the battery. This is especially important for the upper leg, to prevent it touching the battery at the base. The leg that goes into the lower cap then simply needs to be bent back a bit. The other leg should then be bent back in and then back out again, such that the second bend is at about 6 mm from the base of the LED. This is the most crucial measurement. Where the first bend is doesn't matter as much as that it bends upwards sufficiently so the mechanism can push the leg down. AssemblySee the video. Place the LED in the lower cap, then slide the battery in, preferably with the rubber ring at the top. Note that the LED and battery only work one way around, so test that first before assembly (and before bending). Next, place the upper cap by sliding the half ring over the LED-ring of the lower cap at an angle, then move it down at the back. Finally, slide in the slide at the back, with the keyring-holders passing through the vertical slots. Make sure the LED leg goes into the tiny hole of the cylinder. The slide cap will now keep the lower and upper cap together. You might need to slide back and forth a few times to smoothen the sliding surfaces. Now the LED should turn on when you move the slide back. If not, readjust the bends of the LED-legs. To prevent it sliding way back out, effectively disassembling itself, put something throught the keyring-holders. For example a key ring. :)