These kinds of wheels are made of sisal only, stitched, flat-type and dip-treated. The wheels are mounted with a steel center hub, and the wheel can be with a center plate or not.
The dip-treated has 4 hardness and with different colours:
Soft: Yellow (harder than the un-treated one)
Medium: Green
Hard: Red
Rock hard: Purple
Very aggressive and lasts much longer.
Used on an automatic polishing machine to do first-stage heavy-duty cutting and polishing on stainless steel, steel and aluminium etc.. Recommended use with grey, black or brown polishing compound.