ANSI .74 X 1.54 CAT40 45 Degree Retention Knob ~ TPI is M16 X 20. ~ Heat treated alloy steel hardened to HRC 52~56°. ~ ANSI/AMSE B5.50-1994. ~ L is 1.54 ~ L1 is .43 ~ L2 is .12 ~ D is .89 ~ d1 is .74 ~ d2 is .49 ~ A is 45°. TPI is M16 X 20. Heat treated alloy steel hardened to HRC 52~56°. ANSI/AMSE B5.50-1994.