I've been using them every day for many, many years; It's probably the 5th or 6th I've bought. They are made of slightly rubbery plastic that is quite durable. They usually last until I drop something on them and break them. There is usually a small burr in the grooves that needs to be deburred before you can use them. A pocket knife or Xacto knife held along the edge of the groove is usually sufficient to remove the burr. Don't try to cut it as you will take too much material.
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