scope:

This specification is one of a series issued by the Ministry of Aviation either to meet a limited requirement not covered by any existing British Standard or to serve as a basis for inspection of material the properties and uses of which are not sufficiently developed to warrant submission to the British Standards Institution for Standardisation.

This specification covers two grades of material, A and B, of different hardness; Grade B being the harder. The grade must, therefore, be stated on the Order.