Permanent Magnet Brake PMB-398, unused.

https://sepac.com/products/view/permanent-magnet-brake/

Torque Rating (Static): 26.6 lb-ft, (36 Nm)

Body Diameter: 3.98 in, (101 mm)

Overall Length: 2.58 in, (66 mm)

Pilot Diameter-Max: 2.05 in, (52 mm)

Hub Bore Diameter: 1.181 in, (30 mm)