Sewn in spiral rows 1/4" apart with 7 ply sisal. These are used extensively for cutting operations in combination with the 925 Rouge to quickly remove marks left by belt grinding operations. These work best when grouped in 2s or 3s for more stiffness. The RPM should not exceed 2000 RPM. Buff is 1/4" thick. **The outter layer of the wheel now has a very thin piece of linen cloth to keep the sisal from fraying during use.**