The "Rack Type" field in the script window controls the matching between racks and effects when you add racks with the "Racks > Add racks for show..." function, as described in Using “Rack Type” to control what types of racks are used for what effects.  The standard "Rack Type labels" usage for the Rack Type field involves adding a matching label to the Rack Type of effects and racks that go together.  The Rack Type acts as a filter for the rack options when adding racks.  If an effect has a Rack Type of "Banana", then only racks with Rack Type of "Banana" will be suitable candidates for it. "Rack Type part numbers" are another usage of the Rack Type field.  You can put part numbers of racks directly in the Rack Type field of effects, to force the effects into that specific kind of rack.  This usage is similar to  Rack Type labels except: The effect's Rack Type field should contain the part number of the desired rack. The desired rack's Rack Type field should be blank. The effect's type will automatically become compatible with the rack no matter what kind of rack it is -- e.g., you can put a single-shot into a mortar rack or a shell into a single-shot rack. The effect's effective size will automatically become compatible with the rack no matter what the rack's size is. Rack Type part numbers cannot reference an EASYRACK. The major difference between the Rack Type labels usage versus the Rack Type part numbers usage is that the matching labels are purely a filter that limits what racks an effect can go into, whereas Rack Type part numbers automatically resolve any compatibility issues between the effect and the rack with respect to type and size.   Examples A common use case for Rack Type part numbers is putting a slice cake into a single-shot rack.  Normally, a slice cake wouldn't be compatible with a single-shot rack, because the single-shot rack only holds single-shot effects.  But if you put the part number of a single-shot rack in the Rack Type field of a slice cake, the slice cake will become compatible with the rack. Another use case for Rack Type part numbers is putting a single-shot in a cake rack.  In the physical world, some kinds of cake racks are pieces of plywood ("display boards") that you can nail anything to, not just cakes.  So you may want to put single-shots on that type of cake rack.  Rack Type part numbers are the way to do it.   Addressing dialog sort and constraint options Although a Rack Type part number will make an effect's effective type or effective size compatible with the rack, it doesn't change the size or type of the effect with respect to the sorting criteria and constraints in the addressing dialog.  For example, if you use Rack Type part numbers to force a 50mm single-shot into a 3" mortar rack, the effect's size is still 50mm with respect to sorting against other effects. Since the type of the effect isn't changed by Rack Type part numbers, the properties that stem from the type also are not changed (see Why is ‘Type’ so important? What depends on it?).  Cakes, for example, are not considered rotationally-symmetric in Finale 3D, since fan cakes look different depending on their orientation.  Single-shots are considered rotationally symmetric, since they are shot out of a tube without a defined orientation inside the tube. Single-shot racks generally care only about the firing direction of the tubes in the rack but not the orientation of the items in the tubes, since the items are generally single-shots.  But, if you use Rack Type part numbers to force a slice cake into a single-shot rack, the orientation of the slice cake does matter, because the slice cake obviously needs to align with the rows of the rack, physically: a long, skinny slice cake fits into a long, skinny row.  Thus the when the "Racks > Add racks for show..." function adds a single-shot rack to hold slice cakes, it may need to rotate the rack 90 degrees to get the rows to line up with the direction the cake is facing, plus or minus 180 degrees.  The actual requirement is that the sum of the cakes' PAN and SPIN angles is required to match the orientation of the rows in the single-shot rack they are sleeved into, plus or minus 180 degrees. Similar to the sorting fields, the constraints of the addressing dialog, such as "Each module is restricted to a single XXX", refer to the actual type or size of the effects, not to the effective type or size as adjusted by the Rack Type part numbers.   Figure 1 – A Rack Type part number doesn't guarantee the effect goes into the rack, if another effect gets assigned to the rack first!   Rack Type part numbers do not guarantee that the effect goes into the rack.  The Rack Type part numbers automatically ensure the most common compatibility requirements are met, but racks can have other constraints that also come into play, like the size range or fixed angle tubes, or the "Max usable row length" constraint.  If you assign a Rack Type part number to an effect and then when you address the show the effect doesn't end up in the the rack you had assigned it to, one explanation is that the addressing function assigned a different effect to the rack first, taking its spot.  The addressing function assigns firing system addresses and rack tube in the sort order specified in the addressing dialog.  If you want to make sure your Rack Type part number effects get first dibs on the racks you have assigned them to, add the "Has Rack Type Part Number" term to your sorting criteria.  That will guarantee your Rack Type part number effects get the first chance.   Order of collections that Rack Type part numbers can refer to Any single effect collection cannot contain multiple effects or racks with the same part number; they are forced to be unique.  However, when you add racks with the "Racks > Add racks for show..." function, you may be adding racks from any of the loaded effect collections, or from multiple of those collections.  Since part numbers are only forced to be unique within a collection, it is possible and even likely that multiple collections will contain racks with the same part numbers (per-show effects almost always has duplicates from other collections!).  When multiple collections have racks by the same part number, there is a question of which rack a Rack Type part number refers to. Usually, it doesn't matter, because usually when multiple collections have racks with the same part numbers, the rack definitions are the same, but since it is possible that the rack definitions are different, it is important to understand what Rack Type part numbers refer to if you need to troubleshoot racking questions.  The Rack Type part numbers refer to the first matching part number from all collections, sorted by order of: Per-show effects, Generic Effects, My Effects, any loaded effects files, any network inventory that you subscribe to, including Finale Inventories.