Both B7 and B7M are from standard specpfication for alloy-steel and stainless steel bolting for high temperaturer or high pressure service and other special purpose applications.

Both B7 and B7M have the same chemical composition, all equal to Chineses GB grade 42CrMoA

Mechanical properties for A193 B7 and A193 B7M:

Minimum tensile strength 861.25(689.00) MPa, minimum yield strength is 723.45(551.2) Mpa, elongation rate is 16(18)%

Different: B7 max hardness is HB321

B7M max hardness is HB235