Sprue

A sprue is the branching plastic frame that comes out of the injection mould with every part still attached to it. Kits are organized into several labeled sprues, often called runners, with letters or numbers molded into the plastic so instructions can tell you exactly which sprue and part number to find. Keeping sprues in their bag until needed prevents small parts from breaking off and getting lost in the box.

Removing parts cleanly matters as much as the sprue layout itself. A proper sprue cutter leaves a small stub rather than tearing a chunk out of the part, which is the difference between a clean surface and one that needs extra filling later. Many builders cut a part close to the sprue first, then trim the remaining stub flush in a second pass rather than trying to cut flush in one go.

A common mistake is twisting a part off the sprue by hand, which often pulls plastic from the part itself and leaves a rough, stressed area that will not sand out easily. Another is discarding sprues immediately after removing parts, when leftover plastic is genuinely useful for testing paint colors, practicing gluing technique, or scratch-building small details on a later project.