This is a M3 Locking Acorn Nuts. Screw length is 8.5mm. Accurate design. 4 file formats are attached. Details: Pitch: 0.5 mm Height: 8.5 mm Width: 6 mm Thread Dia: M3 (3mm)
Custom size and design possible, you have to contact with me. If you want other file formats please contact with me.
Thanks, Mahbub