Seat knob suit Norton Commando, aluminium alloy, coarse diamond knurl,lightly domed mirror polished face with retaining pin partially fitted. Thread 3/8" UNF [SAE] 24tpi; OD 1.94" 49.4mm; OL 0.925" 23.5mm. Original part number: 060647; 064009 - knurled nut (dual seat)