Firenock CTI Install Guide — Front + Back Carbon Tube Inserts

Firenock CTI (Carbon Tube Insert) is the only system that lets you internally reinforce a carbon shaft while precisely tuning FOC. Front CTI moves balance forward (boosts penetration). Back CTI reinforces the nock end (where lighted nock electronics live).

Sparrow Expeditions is the official US dropshipper for Firenock kits + components. This guide covers install + tuning, with the math integrated into our free Arrow Builder.

What is CTI?

CTI is a precision-OD carbon tube that slides INSIDE your shaft. It reinforces the shaft against torque (less paradox flex), shifts the balance point, and — in the rear position — leaves a clean 2" gap to fit a lighted nock's battery and circuit.

Front vs back placement

Front CTI

• Sits in the FRONT of the shaft, behind the insert
• Centroid: arrow_length − 0.75" (insert offset) − cti_length / 2
• EFFECT: boosts FOC significantly (often +1-3% per CTI)
• BEST FOR: hunters wanting EFOC (12-19% FOC) without changing point weight

Back CTI

• Sits in the REAR of the shaft, 2" forward of the rear cut
• The 2" gap is INTENTIONAL — fits the lighted-nock battery + circuit
• Centroid: 0.5" (nock-to-shaft-back) + 2" (battery clearance) + cti_length / 2
• EFFECT: lowers FOC slightly but reinforces the nock end where impact stress concentrates
• BEST FOR: lighted-nock users + anyone who's blown a nock end on an impact

CTI weight by size

Install procedure

1. Cut the CTI to your desired length (typically 6" or 9")
2. Lightly sand the OD of the CTI with 320-grit to give the epoxy bite
3. Apply a thin band of slow-cure epoxy (NOT super glue — you may need to pull this someday)
4. For FRONT CTI: slide into the shaft until it sits ~0.75" from the front cut (behind the insert)
5. For BACK CTI: slide into the shaft starting 2" forward of the rear cut (leaves battery clearance)
6. Let cure 24h before nocking + shooting

Sparrow Arrow Builder math

Our Arrow Builder models CTI placement and weight in real time. Toggle CTI on/off + front/back, set the length + weight, and watch FOC, total weight, KE, and momentum update live. The math correctly accounts for the 2" battery-clearance offset on rear CTI.

Shop CTI

Sparrow stocks the full Firenock CTI line plus the lighted-nock systems they pair with (NXG2, EP Series, S3 Inverted) across .166, .204, .234, and .246 shaft IDs. Same-day fulfillment on stocked items.

Common questions

Can I run both front and back CTI?

Yes — it's the most stable configuration for lighted-nock hunters who want EFOC. The two cancel out somewhat on FOC, but you get reinforcement at both ends.

Will CTI affect my spine?

Front CTI mass acts like additional point weight for spine calculation — each 25 gr of front-side mass adds ~5 lb effective draw weight. The Sparrow recommender accounts for this.

Does CTI work with all shafts?

Any carbon shaft with a matching ID. Sparrow's Builder filters CTI options by your shaft's ID automatically.