Orton cones are used to ensure the kiln is at the required temperature. Set 3 in the kiln, one lower than the target temperature, one at the target and one higher. This allows you to visibly check the temperature of the firing.

They are available in two sizes:
25mm (1″) mini cones (M)
63mm (2½”) standard size (S)

Price is per bag of 10 Cones. 
25% discount available on 5 packs of the same cone type.