Rockets generally have fins to keep the rocket moving in the same direction. One of the bigger problems in high-power rocketry is mounting the fins to the fin can. There are two alignment goals in mounting fins to the fin can.
- Axial alignment of the fins to the rocket. Misalignment would increase drag on the fins, and would induce unwanted roll, pitch, or yaw, any of which would reduce the maximum altitude of the rocket. The fin jig is match-machined, which will generally prevent any axial misalignment.
- Circumferential alignment of the fins to the rocket. This type of misalignment has much less of a negative impact to rocket performance. An example of extreme circumferential misalignment would be to move one fin next to another (or take one fin completely off), leaving three fins. Many rockets only have three fins to begin with. There would be somewhat less control authority in the pitch and/or yaw axes, but overall impact would be much less severe.