ASTM A193 specification covers alloy steel and stainless steel bolting material for pressure vessels, valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications.
Several grades are covered, including ferritic steels and austenitic stainless steels designated B5, B8, and so forth. Selection will depend upon design, service conditions, mechanical properties, and high temperature characteristics.
Material according to ASTM A193 B7 is often available in national coarse (UNC) thread pitches, if being used in traditional applications, threads are specified 8 threads per inch (tpi) for diameters above one inch.
Below is a summary of a few of the common grades.

High temperature
service

ASTM A193 B5
ASTM A193 B6
ASTM A193 B7          Alloy steel, AISI 4140/4142 quenched and tempered
ASTM A193 B7M
ASTM A193 B16
ASTM A193 B8          Class 1 Stainless steel, AISI 304, carbide solution treated.
ASTM A193 B8A
ASTM A193 B8M       Class 1 Stainless steel, AISI 316, carbide solution treated.
ASTM A193 B8MA
ASTM A193 B8cl2     Class 2 Stainless steel, AISI 304, carbide solution treated, strain hardened
ASTM A193 B8Tcl2
ASTM A193 B8Mcl2  Class 2 Stainless steel, AISI 316, carbide solution treated, strain hardened

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