Spot bridge/differential probes can be referred to as surface probes but are a lower frequency than their high frequency counterparts can be used to find generic subsurface defects. They are normally fitted with a triax detachable connector but can be fitted with a 2 pin microdot or 4 pin Fischer connector.

O.D.         50-500Hz       100Hz-1KHz         500Hz-2KHz           1-10KHz              5-20KHz             20-50KHz
.300"       --------             --------                  SB.3-500H              SB.3-1K              SB.3-5K               SB.3-20K
.350"       --------             SB.35-100H         SB.35-500H             SB.35-1K            SB.35-5K            SB.35-20K
.400"       SB.4-50H         SB.4-100H           SB.4-500H              SB.4-1K              SB.4-5K               SB.4-20K
.500"       SB.5-50H         SB.5-100H           SB.5-500H              SB.5-1K              SB.5-5K               SB.5-20K
.600"       SB.6-50H         SB.6-100H           SB.6-500H              SB.6-1K              SB.6-5K               SB.6-20K
.700"       SB.7-50H         SB.7-100H           SB.7-500H              SB.7-1K              SB.7-5K               SB.7-20K
.800"       SB.8-50H         SB.8-100H           SB.8-500H              SB.8-1K              SB.8-5K               --------
.900"       SB.9-50H         SB.9-100H           SB.9-500H              SB.9-1K              --------                 --------
1.00"       SB1.0-50H       SB1.0-100H         SB1.0-500H            SB1.0-1K            --------                 --------
1.20"       SB1.2-50H       SB1.2-100H         SB1.2-500H            --------                --------                  --------