This is a Taper Shank #M-4071-0072. This shank is designed to secure the probe into a ANSI CAT B5-50 ISO 50 taper machine tool spindle. Shank gauge length is 35.30 mm (1.390 inches), and it is suitable for OMP40 and OMP400 probes.
Taper shank: shank specification ANSI CAT B5.50-1985 (imperial pull stud thread), taper ISO 50
M-4071-0072 | Machine Tool Probes | Taper Shank | CAT50 | Renishaw