Relates to length bars of the cylindrical type, in inch sizes up to 48 inch and metric sizes up to 1200 mm, having parallel end faces finished by lapping. If longer bars are required, they shall be uniform in diameter and straight overall to the limits laid down in Clauses 7 a and b; tolerances for flatness and parallelism of faces shall be proportionate to those specified in the appropriate Tables 1 to 8, and their lengths shall conform to the requirements of Clause 7d. Provision is made for two designs of lenth bar, one with complete plane faces and the other with annular faces surrounding an internally threaded hole at one end or both ends of the bar.