From the top of the spool holder to the bottom of the lower panel where the spool sits is about 125mm so assuming that the inside mounting hole is 50 to 55mm then the max diameter would be 200mm. The max spool width it can take is roughly 85mm. In my experience with the sigma the diameter of the spools is not an issue, only the width as they have to fit in the vacuum formed cavity of the bottom panels. For wide spools I place them against the side panel with half of it inside the cavity, not ideal but it works. Try not to get wide spools like the 90mm you find on cheap filaments.