An herb grinder is made out of metal like aluminum or wood to grind herbs and spices into small pieces, so they can be added to food and eaten. Some types of herb grinders are very good at grinding marijuana buds into smaller size particles.
Herb grinders used to prepare marijuana are also called bud grinders. After properly grinding marijuana with an herb grinder, it will burn more evenly when rolled into a joint. And because it is broken down into small particles, it will not poke holes in rolling paper or pre rolled cone.
The smaller particles of marijuana are suitable for rolling into a joint, smoking in a pipe or vaporizer, sieving to produce hash, or for some purpose that requires finely ground marijuana.
If you break up marijuana with your hands or with scissors prior to rolling it into a joint or using it in some other way, you should try using an herb grinder instead. Prior to first using one, I thought they were some kind of toy that ...
