The warp thread counts given on that site are basically a description of the colour and number threads you would need when designing your tartan warp. They are about colour - not the weight of the yarn. You could make your warp out of fine merino, thick wool or ????? depending on what you want to create. You will have to plan your project around the number of repeats of the pattern/thread count are needed to make the project you plan to weave. Hope this helps.