Pack of two Panasonic microwave oven waveguide covers 

Part number: Z20556S10XP

Dimensions: length = 117mm, height = 58mm.

If your microwave is arcing or sparking during cooking, it may be that the waveguide cover is damaged. This metallic type material, which is a blend of mica and is invisible to microwaves, it covers the aperture that the microwaves pass through to get into the oven cavity. When old damp or contaminated can react to microwaves by arcing.  

1. NN-SD279SB, NN-SD277SB, NN-GD376SB,  NN-SD258WB, NN-SD278SB, NN-SD268MB, NN-SD259WB, NN-SD269MB, NNSD279SB, NNSD277SB, NNGD376SB,  NNSD258WB, NNSD278SB, NNSD268MB, NNSD259WB, NNSD269MB.