My tool is a small hex key in which you can put on an external sleeve to fit different ends. It is in metric but can be converted to English. It is small and is easily replaceable if it breaks. It is made out of abs so it is durable but light and it can withstand the stress of cranking. Each sleeve fits over the next and if you wish to print bigger you can. To put the next attachment on you just slide it over the tool after having lined up the edges.