M4 x 10mm 'TCI' Notched-Head Screw This is the TCI ("testa con intaglio," or "head with notch") screw used on old Gaggia lever group tension springs, the upper burr on a Rancilio MD-50 grinder, the inner grinder burr screws on a Nuova Simonelli Mythos, and the Fiorenzato MC flat burrs. COMPATIBILITY Fits: Gaggia lever group tension springs (older models); Rancilio MD-50 upper burr; Nuova Simonelli Mythos inner burr; Fiorenzato MC flat burrs INSTALLATION Standard screwdriver swap, though burr-mounting applications should be tightened evenly in sequence to avoid warping the burr carrier. PRO TIPS This shows up on both grinder burr carriers and older Gaggia lever springs, two completely unrelated applications, so double-check which assembly you're servicing before ordering the quantity you need, since burr jobs typically need three or more and the Gaggia spring application needs far fewer.