Summary This fits a utility razor blade. It is an interference fit and I recommend a vise and mallet to install for safety. Place the blade in a vise and start one side of the holder at an angle. Then finish installing by ensuring it's centered (because there are two pins printed inside to align the blade on and help keep it steady) and using a mallet to seat it fully without going to far and breaking the handle. It's proven to be an extremely sturdy tool thus far, printed in PLA at 100% infill. I designed this for scraping prints off a glass bed, not for heavy duty use. Use at your own risk.