Intended for modeling.55 mm long. the shaft is unthreaded, but machine variance will still probably make the threads on a 8mm nut still catch.This is useless for anything but reference and model making.If you have a hobbling rig, maybe use them for practice.This was tricky to get to print right. start out hot, then set the extruder temp down to barely extrudable after its a few rows up the shaft. If you don't it will be a blob of uncooling plastic about an inch up. It took a fan. Running it this cool will make a good print, but it won't have any tensile strentgh and will easily snap.