In a pinch, I needed a very narrow hex key extender that could fit into a small hole. I designed it to be as narrow as possible. When I printed it, it cracked when I inserted the hex key, but it still held its shape and allowed me to tighten the screws I needed to. It’s very useful in a crisis, but it might not be a reliable tool for long-term use.

It’s about 68 millimeters long, with the extended part being around 58 millimeters. The diameter is 8.4 millimeters.

I recommend inverting it and printing vertically (with the part facing the screwdriver or drill bit pointing downward) — this will take longer and require the use of a border, but it will ensure no support is present in parts that require tight fit/good tolerances.