This discussion has been joined by several people who have hands on knowledge of the Hi-Lok fastener system through their employment in ?big airplane? companies. I too have decades of ?big airplane? employment and like them, have buckets of surplus Ti fasteners. I also agree with them wholeheartedly that proper hole prep is paramount to a properly engineered shear connection. In an interference fit such as used in the center section bolts, an out of round or oversized hole will destroy the strength of that connection, no matter what material the fastener is made of.
In short, a perfectly round, reamed to correct interference fit hole is required whether you are using an exotic Ti Hi-Lok or an AN bolt from Spruce. The precision of the hole is the key to strength (assuming the pin meets minimum engineering specifications).
That said, I take exception to the cautions in this thread that seem to imply the Hi-Lok pin is somehow less tolerant of perfection than an AN bolt. It is true that Hi-Loks are a specialty fastener and the ?big airplane? companies like mine require training on their installation, but that is true of almost EVERY critical operation found on the shop floor. The Hi Lok system is in many cases a direct replacement for a traditional permanent bolted connection, and it?s not a difficult process to learn. Here?s what the company?s website has to say:
The HI-LOK? Fastening System:
? is basically a threaded fastener which combines the best features of a rivet and a bolt. It consists of two parts, a threaded pin and a collar
? is rapidly and quietly installed by one person from one side using standard power tools or hand tools with less worker fatigue than with either regular rivets or bolts.
? easily adapts itself to large scale production in a variety of pin and collar material combinations for high strength and high temperature performance.
A bolt and nut system is heavier than the HI-LOK? Fastening System. Minimum weight results from elimination of the wrenching surfaces on a bolt and nut system. Wrenching clearances are minimized and great weight savings result from the design of more compact structural joints.
Bolt and nut systems require calibrated torque wrenches and torque inspection. The HI-LOK? Fastening System eliminates these concerns.
So, the bottom line as I see it: When it comes to hole prep for a critical shear connection, ?Perfection? is the standard we should strive for; regardless of the fastener system we are using. If any of our more experienced shop personnel have a reason why a Hi-Lok pin is more intolerant of a properly prepared hole than an AN bolt, I?d sure like to hear it. I?m always ready to learn something new.
As for ?worth it? regarding the cost vs. weight savings, that?s for the individual to decide. As has been discussed, these can be acquired for a huge range of pricing from ?free? to ?eye watering?. And even if you have to pay full price, spending $500 bucks to save a pound on your center section bolts is far better money spent than an exotic, multicolor paint job (IMHO).