The phrase "thick line" is correct and usable in written English.
You can use it to refer to a line that has more width than usual, for example: "She used a thick line to outline the shapes on her drawing."
Without the metamaterials, the microscope showed only one thick line.
GalbraithShaplen tries to draw a thick line under Kreuger's legacy.
A thick line to indicate a load-bearing wall?
There is some off-white cheese poking out, along with a thick line of sauce.
Shouting "We want to cross!" and "Let us pass!" the crowd pushed against a thick line of state security officers.
Moqtadah al-Sadr's followers were assembled in a thick line that snaked out the office door and through the atrium.
Spoon the potatoes over the turkey, mostly in a thick line towards the centre of the meat.
cold cathode: thick line.
Thick line indicates the profile of the seismic survey.
The thick line corresponds to the median sale values.
The thick line indicates the profile of the seismic survey.
