Attachment points have special and strict protocols in Starcraft II, if you doesn't use them correctly, the model will have weird issues. This tutorial is a summary of the ruler of attachment points. I hope it can help you when you are using Blender or 3dsmax.
1) You can only use the name in the list, custom names are illegal. (the list is attached at the end of this tutorial.)
Example: Pos_Hill is legal, Pos_DustinBrowder is illegal;
You can't use custom names.
Example: Ref_Attacher 01~19 is legal, but Ref_Attacher 20 is illegal;
Example: Ref_Head is legal, but Ref_Head 01 is is illegal.
Example: Ref_Weapon Left is legal, but Ref_Weapon Left 01 is is illegal.
You can't add numbers at the end of the Attachment points unlimited, each kind of Attachment points has its own upper limit.
2) Avoid duplicate names.
When you added an Attachment volume, the relevant Attachment point will be created automatically.
Example: If you add Vol_Target to the model, you shouldn't create Ref_Target, for the art tool will create Ref_Target itself at the center of Vol_Target.
The Ref_XXX is equal to Ref_XXX 00.
Example: If you have Ref_Head, you shouldn't add Ref_Head 00 at the same time.
3) Special names should be used only at the specified situation:
Ref_Attacher, this attachment point is used for taking control of the parent bone. For example, the tail of Viper, actor system needs Ref_Attacher to control the movements of the tail.
(Btw In the beam models, at the end of each beam, there is a helper called "Attacher", Helpers with special names in SC2 can cover the original animations.)
Ref_Turret, Ref_TurretY Ref_TurretZ, these attachment points are used for standard turret behavior in SC2. A standard turret unit likes siege tank has only one turret. At this situation, using these attachment points can conveniently build your own turret unit.
If you want more than one turret, you can't use these attachment points. Instead, you can use other attachment points/Bones, and set their turret behaviors in behavior editor, each attachment point/Bone can be a turret point if you correctly set their behaviors.
Vol_Shield (Ref_Shield), Vol_Shield is used to define the area of shield for Protoss units, it should be a sphere with Scale on X, Y, Z directions. Once Vol_Shield is added, the Ref_Shield will be created at the center of the sphere.
Ref_StatusBar, Ref_StatusBar is used to define the health bar location of the model (if this attachment exist.)
Vol_Target (Ref_Target), Used for defining the location that the missiles should hit and the impact effects should be played, usually it's not a point but an area, so Vol_Target is much convenient and common than Ref_Target when you are making a model.
Ref_Weapon, used for weapon launch.
Ref_Damage, used for damage effects, like the fire on the damaged buildings.
Ref_Origin, located at the original point, used as the reference of a lot of events in SC2. Ref_Center, located at the middle part of the model, used as the reference of a lot of events in SC2, such as the Buff effects around the body.
Ref_Overhead, located at over head location of the model, used as the reference of a lot of events in SC2, such as the Buff effects like stun.
Ref_Hardpoint, used to attach other models, likes medivac carries the Thor. Ref_Hardpoint is the reference location that Thor attaches to the medivac.
4) Attachment Volume can only be special geometries, usually Sphere, cylinder, box and capsule, these geometries are scalable, you can check the art tool help documents for more details.
The list of all legal attachment points in starcraft II (305 in total. This list was summarized in 2013 by Renee, so maybe some new attachment points were added later, but I still suggest that use the names in the list, don't use custom names only if you know they are legal in Starcraft II.)
Pos_SetLocation Pos_SetLocation 01~15 Pos_RaynorToTychus Pos_TychusToRaynor Pos_RaynorToHorner Pos_HornerToRaynor Pos_RaynorToHanson Pos_HansonToRaynor Pos_RaynorToTosh Pos_ToshToRaynor Pos_RaynorToSwann Pos_SwannToRaynor Pos_RaynorToAdjutant Pos_AdjutantToRaynor Pos_Raynor Pos_Tychus Pos_Horner Pos_Hanson Pos_Swann Pos_Adjutant Pos_JessicaHall Pos_MarcusCade Pos_Warfield Pos_Hill Pos_Merc03 Pos_Tosh Pos_Firebat Pos_SiegeTank Pos_Dropship Pos_Viking Pos_Spidermine Pos_Ghost Pos_Banshee Pos_Marauder Pos_Stetmann Pos_Marine Pos_Bartender Pos_Kerrigan Pos_EvolutionMaster Pos_Zagara Pos_Primal Pos_ProtossScientist Pos_Stukov Ref_Origin Ref_Center Ref_Attacher Ref_Attacher 01~19 Ref_Damage Ref_Damage 01~19 Ref_Elevator Ref_Engine Ref_Hardpoint Ref_Hardpoint 01~19 Ref_Hardpoint Left Ref_Hardpoint Right Ref_Hit Ref_Hit 01~09 Ref_Mount Ref_Overhead Ref_RallyPoint Ref_Shield Ref_StatusBar Ref_StatusBar 01~19 Ref_Target Ref_Target 01~40 Ref_Target Final Ref_Target Heavy Ref_Target Light Ref_Target Medium Ref_Target Shield Ref_Transmission Ref_Turret Ref_TurretY Ref_TurretZ Ref_Upgrade Ref_Upgrade Armor Ref_Upgrade Engine Ref_Upgrade Engine Bottom Ref_Upgrade Engine Left Ref_Upgrade Engine Right Ref_Upgrade Weapon Ref_Upgrade Weapon Bottom Ref_Upgrade Weapon Left Ref_Upgrade Weapon Right Ref_Weapon Ref_Weapon 01~30 Ref_Weapon Bottom Ref_Weapon Left Ref_Weapon Right Ref_Agria Ref_Aiur Ref_Albion Ref_Avernus Ref_BelShir Ref_Castanar Ref_Char Ref_Dylar Ref_Haven Ref_Korhal Ref_MarSara Ref_Meinhoff Ref_Monlyth Ref_Moria Ref_NewFolsom Ref_PortZion Ref_PU72516J Ref_Redstone Ref_Tarsonis Ref_Tyrador Ref_Umoja Ref_Valhalla Ref_Xil Ref_Back Ref_Chest Ref_Chest Left Ref_Chest Mount Ref_Chest Mount Left Ref_Chest Mount Rear Ref_Chest Mount Right Ref_Chest Right Ref_Chin Ref_Face Ref_Foot Left Ref_Foot Left Rear Ref_Foot Right Ref_Foot Right Rear Ref_Forearm Left Ref_Forearm Right Ref_Hand Ref_Hand Left Ref_Hand Right Ref_Head Ref_Head Top Ref_Head Mount Ref_Knee Left Ref_Knee Right Ref_Lip Upper Ref_Shoulder Left Ref_Shoulder Right Ref_Waist Back Ref_Waist Front Ref_Waist Right Ref_Waist Left