Stud, for cylinder head to barrel, Norton alloy head twins, 3/8 in x 26tpi x 3/8 in x 22tpi (BSF screwed into the cylinder head). 3 required per engine. ZP Original part number: K12/977; 18756; 24389; NM24389; 067885; 06-7885 - cylinder head and barrel stud (front and rear) 3/8