These all items are made out of
Steatite C-221.

STEATITE - C221
Basically magnesium silicate
Impervious material structure
Very good Mechanical Strength
High volume resistivity upto 1000 degree C.
Low dissipation factor
Good dielectric strength
Very popular

Beads are used for insulation of wire where, plastic coating can not be used.

MCB Plates are used in MCB to prevent arc from reaching plastic body.

Cartridge Heaters and End Seals are used at the end portion of Thermocouple or Heaters as Insulator.

Band Heaters are used in covering heating coil in Band Heaters.

Thermostat and Lamp Holders are made out of C-221 Steatite and basically are Insulators.