I took a photo of ShuGang's 211 and 805A which were manufactured recently.
The photo is located at below URL.
http://userdisk.webry.biglobe.ne.jp/013/400/99/N000/000/000/129022284759516122098_211vs805A.jpg
I understood the difference between 805A (Mu=50) and 211 (Mu=12.5)
comes from the dimensions of Grid-Filament, Grid-Plate and Grid winding pitch.
The photo is located at below URL.
http://userdisk.webry.biglobe.ne.jp/013/400/99/N000/000/000/129022284759516122098_211vs805A.jpg
I understood the difference between 805A (Mu=50) and 211 (Mu=12.5)
comes from the dimensions of Grid-Filament, Grid-Plate and Grid winding pitch.