They do wear out and eventually the velcro doesn't stick to the abrasive very well. However, I've found that the life can be extended considerably by turning the speed to its lowest setting. At high speed the velcro just melts and in 5-10 minutes becomes useless. At the lowest speed the velcro stays intact and I end up ordering replacements every few months. This holds true for the larger triangular sheets.Keep the speed to a minimum and they will still out sand any other tool I own.
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