Bolt cylinder head, Norton twins (ea). Outer head bolt by spark plugs, 4 required. Head 3/8BSF, 3/8 x 26tpi x 2-5/16in . Pre 750 head. These fit iron heads and alloy heads. The bolt heads are 3/8 in BSF and were reduced in head size after early Commandos. Atlas heads have a different size bolt. Original part numbers: D12/972; T2096; 060401; 06-0401 - cylinder head and barrel bolt (long) 3/8"
