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Specification for use in precision locating, layout and inspection works
Federal Specification for granite comes under, GGG-P-463C. This specification was approved by, The commissioner, Federal supply service, General service administration. For the use of all federal agencies.

This specification covers igneous rock (granite) surface plate for use in precision locating, layout and inspection works. Federal specification does not include all styles, grades and sizes of the commodity indicated by the titles of the specification. But are intended to cover only those generally used by the Federal government.

Style :
Rectangular – No lip
Rectangular – 2 lip, In either direction
Rectangular – 4 lip
Round – No lip
Grade :
Grade AA
Grade A
Grade B
Surface plate covered by this specification shall be made of fine or medium grained igneous rock. Such as Biotite granite, Biotite hornblende, Diabase, Hypersthene gabbro, muscovite biotite/granite-gneiss, etc.

The material shall be free of seams, or other defects, which may affect the serviceability of the surface plate. Other granite are acceptable provided, they meet the requirements of this specification and are in accordance with ASTM (American Society for Testing and Materials)

Design and Construction:
The design and construction shall be such that the surface plate is free from any defects, which may render it unserviceable.

Thickness and Stiffness:
The surface plate shall have a thickness capable of supporting a total normal load equal to 50 pounds for each square foot of surface plate area loaded in the center of the plate without deflecting the plate along a diagonal or diameter more than one-half the flatness tolerance.

Recommended minimum thickness for normal loading at 50 pounds per square foot on rectangular plates on three supports.

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