Red spirit-filled thermometers provide increased safety and economic pricing. They contain a petroleum-based column with red dye, which is significantly safer than mercury. These thermometers all have 6- to 7-mm outer diameters, and the bulbs have equal or smaller diameters than the stems. They are graduated in 1° C, or both 1° C and 2° F. Lines and numbers are permanently fused to the glass.