[wanted2411]

    COLLISION_GROUP_NONE  = 0,
    COLLISION_GROUP_DEBRIS,            // Collides with nothing but world and static stuff
    COLLISION_GROUP_DEBRIS_TRIGGER, // Same as debris, but hits triggers
    COLLISION_GROUP_INTERACTIVE_DEBRIS,    // Collides with everything except other interactive debris or debris
    COLLISION_GROUP_INTERACTIVE,    // Collides with everything except interactive debris or debris
    COLLISION_GROUP_PLAYER,
    COLLISION_GROUP_BREAKABLE_GLASS,
    COLLISION_GROUP_VEHICLE,
    COLLISION_GROUP_PLAYER_MOVEMENT,  // For HL2, same as Collision_Group_Player
                                        
    COLLISION_GROUP_NPC,            // Generic NPC group
    COLLISION_GROUP_IN_VEHICLE,        // for any entity inside a vehicle
    COLLISION_GROUP_WEAPON,            // for any weapons that need collision detection
    COLLISION_GROUP_VEHICLE_CLIP,    // vehicle clip brush to restrict vehicle movement
    COLLISION_GROUP_PROJECTILE,        // Projectiles!
    COLLISION_GROUP_DOOR_BLOCKER,    // Blocks entities not permitted to get near moving doors
    COLLISION_GROUP_PASSABLE_DOOR,    // Doors that the player shouldn't collide with
    COLLISION_GROUP_DISSOLVING,        // Things that are dissolving are in this group
    COLLISION_GROUP_PUSHAWAY,        // Nonsolid on client and server, pushaway in player code

    COLLISION_GROUP_NPC_ACTOR,        // Used so NPCs in scripts ignore the player.

Collision Group Types. Find what you want and use this.