Panasonic commercial air filter mounting lug. 

Panasonic part number: ANE90828U0AP
This is the securing lug fitted to the oven that the open end of the air filter locates into.
The knurled screw at the other end is supplied with the air filter.

Suitable for:
Panasonic NE-1843 (NE1843) commercial microwave ovens,
Panasonic NE-1853 (NE1853) commercial microwave ovens,