O-RING 02037. Replaces part (same size as) EPDM rubber version M_71. There are more than one application for this o-ring (originally used and designated for the Mairali, thus the 'M' part number), for example, the Rancilio Z11 RE manual group and steam valves, Futurmat water expansion valve o-ring as well as the super old Carimali steam and water valve shaft o-ring.
In most applications, food-safe lubricant is required.