Class Mods, or COMs (short for Class Optimization Modules), are influential items in Borderlands. They are class specific upgrades that provide benefits to the character (or the entire team) by offering a wide variety of bonuses such as amplifying a character's damage, healing, increasing character health or shield capacity, reducing reload times, increasing skill ranks, etc. Class mod skill bonuses do stack, even if a specific skill is maxed (5/5), up to a total maximum of 9 ranks in any skill. A skill bonus however will not function unless the character has at least 1 point invested in the specified skill.