FS-2.26" BBX 38mm vs FS-2" IRIS 29mm: Which Fin Set Fits Your Build?

The deciding factor is your airframe, not the fin count

Both the FS-2.26" BBX 38mm and the FS-2" IRIS 29mm are four-fin sets from LOC Precision, so the choice comes down to which rocket you are building. The BBX set is designed for the 2.26" BBX 38mm rocket, while the IRIS set is designed for the 2-inch IRIS with a 29mm motor mount. If you already own one of these rockets, the matching set is the straightforward pick. If you are planning a scratch build, use the airframe diameter and motor mount size as your first filter.

Side-by-side: BBX 38mm vs IRIS 29mm fin sets

• FS-2.26" BBX 38mm: Designed for the 2.26" BBX 38mm rocket; includes four fins; made for high power model rocketry applications; brand LOC Precision.
• FS-2" IRIS 29mm: Designed for the 2-inch IRIS rocket with a 29mm motor mount; includes four fins per set; suitable for high power rocketry applications; brand LOC Precision.

What the BBX 38mm fin set gives you

• FS-2.26" BBX 38mm: Includes four fins for a 2.26" diameter rocket tube. A complete set for one rocket, so you can plan the build without ordering extra fins.

  

• FS-2.26" BBX 38mm: Compatible with the BBX 38mm model. Confirms the intended airframe and motor mount size, which is the key fit check before ordering.

What the IRIS 29mm fin set gives you

• FS-2" IRIS 29mm: Includes 4 fins per set. Matches the four-fin configuration of the IRIS build.

  

• FS-2" IRIS 29mm: Compatible with 2-inch IRIS models featuring a 29mm motor mount. Ties the set to a specific airframe diameter and motor mount, preventing a mismatch.

When the 38mm BBX set is the right choice

Choose the FS-2.26" BBX 38mm set if you are building or repairing the BBX 38mm rocket. The 38mm motor mount indicates a larger airframe than the IRIS, and the fins are sized for that 2.26" tube. This set is also a direct replacement if you need to swap damaged fins on an existing BBX. Keep in mind that the supplied information does not include fin dimensions, material thickness, or installation instructions, so verify fit against your actual airframe before assembly.

When the 29mm IRIS set is the right choice

Choose the FS-2" IRIS 29mm set if your project is the 2-inch IRIS with a 29mm motor mount. The smaller airframe diameter and motor mount make this a distinct set from the BBX, and the four fins are intended for that specific model. As with the BBX set, the catalog does not list fin span, thickness, or step-by-step mounting guidance, so treat the compatibility statement as your primary fit check and confirm against your kit's parts.

What the catalog does not tell you

Neither product record includes fin dimensions, weight, material specification, or installation instructions. That means you cannot compare the two sets by fin area or thickness from the supplied information alone. If you are choosing between the two for a scratch-built rocket, the airframe diameter and motor mount size are the only confirmed differentiators. For a replacement on an existing rocket, match the set to the model name and motor mount listed in the compatibility statement. When in doubt, measure your airframe's outside diameter and motor mount tube before ordering.