The term sprue has two related meanings.
- In molding, it refers to part of the network of channels that distribute material to parts of a mold. Material (molten plastic or die-casting alloy in the case of Transformers toy) enters the mold through the large sprue, is distributed to the mold cavities through smaller runners, and enters individual cavities through gates. Sometimes this whole system of sprue, runners, and gate is called the sprue system or runner system.
- On the molded part, the term "sprue" is often applied to the material which solidified inside the sprues, runners, and gates, and remains attached to the part until it is trimmed away, usually to be discarded. This is the more common use among Transformers fans. This usage is synonymous with the term 'tree', as it applies to molded parts.
Parts are often left attached to their sprues when Transformers are sold as kits. Weapons of otherwise assembled toys may also be packed this way. Sprues can be an excellent and cheap source of small plastic rod for kitbashing, which can be quite nice if one has already spent all available funds on Toraizer.
- Runner System - Explanation of the parts involved in this discussion.