A 2-part bobbin. 15 mm long (inside) and 21 mm long (outside). Diameter about 16 mm. Designed to take a 5 mm diameter ferrite rod. It turns out the transformer I wound on this was nowhere near as good as I wanted (probably due to the incomplete magnetic path) but it may be useful to someone anyway!Prints as 2 parts with no support. 0.4 mm nozzle, 0.2 mm layers. Once printed, the top part of the bobbin is superglued to the bottom (superglue sticks PLA very well). Note the taper directions to match up the top of the bobbin with the main section. I found that the fit was perfect with my print settings (probably 80% infill but can't remember!).