This is a Taper Shank BT40 #M-4071-0057. This shank is designed to secure the probe into a BT ISO 40 taper machine tool spindle. Shank gauge length is 32.00 mm (1.260 inches), and it is suitable for OMP40 and OMP400 probes.
Taper shank: shank specification BT-1982, taper ISO 40
M-4071-0057 | Machine Tool Probes| Taper Shank | BT40 shank for OMP40 and OMP400 | BT40 | Renishaw