Solution
Match 553 / 441 / 421 to the iron, aluminum, and calcium limits you actually buy against
Silicon metal grades are named by the Fe / Al / Ca impurity limits, not by a single silicon percentage. Ordering the wrong grade wastes money or fails the melt spec.
Approach
Source product pages list 553, 441, and 421. The grade article also lists 411, 3303, 3305, 2202, 2502, 1501, and 1101 as industry grade names. Confirm the exact Fe / Al / Ca table against the purchase order — the live product pages do not publish a full impurity table for each grade.
SizeSee product pages
PackingSee product pages
Grade naming system from silicon-metal-grade article. Do not invent Fe/Al/Ca maxima that are not on the source pages.
Silicon Metal
Industrial silicon (~98% Si) for aluminum alloys, special steel and silicones
Silicon Metal 553
Grade 553 industrial silicon for aluminum, special steel and silicone plants
Silicon Metal 441
Grade 441 silicon metal for tighter Fe / Al / Ca control than 553
Silicon Metal 421
Grade 421 silicon metal for aluminum, special steel and silicone duty