2.63 Harpoon Fin Set Alternatives: Phoenix vs PK-57 V2 Fit
By High Power Model Rocketry | Published: 2026-11-03
Category: Comparisons
Compare the 2.56" TWT Phoenix fin set and PK-57 4" V2 fin set as alternatives for your 2.63 Harpoon build. Get fit guidance and trade-offs before you buy.
Quick answer
For a 2.63 Harpoon build, the 2.56" TWT Phoenix fin set is the closer match in diameter, while the PK-57 4" V2 fin set is sized for 4-inch V2 kits and will need adaptation. Choose Phoenix for a straightforward fit; choose PK-57 only if you plan to modify the airframe or use it on a different project.
Why diameter match matters more than shape
The Harpoon's 2.63-inch airframe sets the fin root chord and span you can work with. A fin set designed for a different diameter may still be usable, but you'll likely need to adjust the root edge or add material. The Phoenix set is intended for 2.56-inch tubes, so the difference is small enough to manage with minor sanding or a thin shim. The PK-57 set targets 4-inch V2 kits, so its root dimensions are substantially larger and won't drop into a 2.63-inch Harpoon without rework.
Mounting method and hardware compatibility
The Phoenix fin set is designed for slotted tubes with a tube coupler backing, so it assumes you have internal backing for the fin tabs. The Harpoon kit includes a pre-slotted airframe, but you should confirm the slot width and tab depth match the Phoenix fins before committing. The PK-57 set is a replacement for LOC Precision V2 kits and doesn't specify a mounting method in the catalog, so treat it as a blank component that may require custom slots or through-the-wall conversion.
When a different fin set makes sense
If you're building a scale Harpoon and want to stay close to the original outline, the Phoenix set's smaller size is a better starting point. If you're experimenting with a stretched or upscaled Harpoon, the PK-57 V2 fins could work as a base for a larger build, but expect to cut them down. Neither set is a direct replacement for the Harpoon's included fins, so plan for some fitting regardless.
Trade-offs at a glance
- Diameter fit: Phoenix is sized for 2.56-inch tubes, close to the Harpoon's 2.63-inch airframe; PK-57 is for 4-inch V2 kits, a much larger diameter. Measure your airframe diameter and compare to the fin set's intended tube size before ordering.
- Mounting requirements: Phoenix assumes a slotted tube with coupler backing; PK-57 does not specify a mounting method, so you may need to create your own slots or backing. Check that your build has the internal structure to support the fin set's mounting style.
- Modification effort: Phoenix may need minor sanding or shimming to fit 2.63 inches; PK-57 will likely need substantial trimming or a different airframe. Choose the set that matches your comfort level with cutting and fitting fins.
Product facts
- 2.63 Harpoon: Includes pre-slotted airframe, laser-cut fins and rings, 28-inch rip-stop nylon parachute, Kevlar shock cord mount, and vinyl decal set. The kit supplies most recovery and airframe hardware, so you only need a fin set if you're replacing damaged fins or customizing.
2.63 Harpoon - 2.56" TWT Phoenix Fin Set: 2.56" TWT Phoenix Fin Set - 1/8" thick, designed for slotted tube with a tube coupler backing, quantity 4 aft / 4 forward. The 1/8-inch thickness suits 2.56-inch tubes, and the coupler backing requirement means you need internal support for the fin tabs.
2.56" TWT Phoenix Fin Set - PK-57 4" V2 Fin Set: PK-57 4" V2 Fin Set includes four fins for 4-inch diameter V2 rocket kits. These fins are sized for a larger airframe, so using them on a 2.63-inch Harpoon will require significant modification.
Which fin set should you choose?
Best for
- Builders who want a close diameter match for a 2.63 Harpoon with minimal modification.
- Those with slotted tubes and coupler backing already in place.
Not for
- Builders who need a direct drop-in replacement for the Harpoon's original fins.
- Projects where the airframe is not slotted or lacks internal backing.
