Checkline SB [SB6] 6-Step Steel Test Block, 0.050 / 0.100 / 0.250 / 0.400 /0.600 / 0.800 Inch - Uncertified, Supplied In Wood Case. The SB6 is a 6-Step Test Block fabricated from 1018 Steel (without Certification) for convenient confirmation of thickness gauge calibration, when NIST-Traceable Calibration Step Blocks are NOT REQUIRED. Supplied in a in felt-lined wood box.