I've never thought a torque key made much sense on a banjo. Getting the torque equal on all the nuts is only going to give you an even tension on the head if all the threads are clean and lubed, the bearing surfaces of the nuts and shoes/flange are correctly aligned and smooth, the neck isn't pinching the tension hoop, the head bearing surface is smooth, and a bunch of other fiddly bits are working just right.

What Dan said. You want to measure head tension (or deflection), not nut torque. And you want the tension or deflection to be even around the head.

I certainly agree with what has been stated, but being a belt and suspenders kind of person about some things, I use an inch-pound screwdriver to start things off. For me, it helps to keep the process going evenly. Also, it helps to spot several conditions like those mentioned above and others that might be limiting the overall tone quality of the banjo or durability of the components.

The amount of force generated by a screw thread is related directly to the pitch of the thread (threads per inch in the English system or thread spacing in millimeters in the Metric system.) and the torque being applied. The actual head tension is the result of many factors, but the total force generated by the screws has by far the greatest effect.

For that reason, I tension the screws evenly to get the head tensioned to approximately where I think it should be by pressing on the head or thumping it and watching to make sure that the hoop is even all around. At that point I switch to a Drum Dial device and tune the head tension as evenly as possible, checking in 8 evenly spaced locations.

Sometimes this requires a surprising amount of adjustments to get the head tension as close to equalized as practical. This reflects the fact that many other factors are involved. Then, If I feel like chasing details, I use an electronic tuner to adjust the head tension to a specific pitch. I quess my process is actually a belt and suspenders approach with a piece of rope and some safety pins thrown in!

I’ve never used the torque key mentioned, but have used a torque wrench. As a lifelong mechanic, I have whatever tools I could ever want. But, I’ve gotten away from using torque on banjo heads, because the condition of the threads and mating surfaces just isn’t consistent enough. I’ve even gone simpler. Once I get the head evenly snugged up, with a level tension hoop, and all nuts at finger tight contact… I count turns… going 1/4 turn on each nut, until the head feels good and sounds good. Then I get the drum dial out, and make it perfect all the way around.

My experience, once I got my drum dial, after trying every other method, was how uneven the head tension could be, with even torque, and how varied the torque could be, with even head tension. Even without a drum dial, my experience told me that counting turns was more accurate than torque. Also keep in mind that the head manufacturing is not always even, or consistent, and drum dial tension is a way to get a flakey head even, without guesswork. And if you are working with cheaper banjos with thin rims that could be warped, or an old Goodtime with a big blobber weld and imperfect tension hoop, who knows what kind of variables you are dealing with.

I have not used this particular torque key Kentucky5 but it sure looks intriguing. Let us know if you get one and how well it works. It would be nice to hear from someone who has used one.
It even has a built in torque knob to adjust the break away when you get to the desired tension. Way cool.
Kent
(I’m a sucker for gadgets) lol

At the low torque involved, too many factors come into play unless all parts are precision and banjo hooks/nuts are far from precision. I tried the torque wrench almost 50 years ago and found it to be unsatisfactory unless you wanted busted heads. Keeping the hoop level is a much better guide.

All excellent advise w/ one more comment I'll add , the machining & plating specs of threaded parts , is a spec known only by the manufacturer . My experience w/ this process has been somewhat involved in my career , especially involving government & military specs .
I don't believe there are many , if any, machining or plating specs used w/ banjo parts which leaves friction wide open between threaded parts .
So my point is , torque values dependent hugely upon friction in mating threaded parts w/ wide open specs can be difficult to manage . Larger thread torque values are easier & cheaper to control .

Even if a torque wrench could provide a measurement that is precisely proportional to the longitudinal force applied to the tension hooks, I think that doesn't assure that uniform head tension can be achieved. I believe this is because of the lack of precision in the construction of banjo head itself and the way it reacts to the applied forces. Because of the lack of precision in the head construction, I suspect that different amounts of force must be applied to the tension hooks to achieve the same amount of head tension adjacent to each hook

This is why I believe that the drum dial is the most effective available tool for achieving uniform head tension. The drum dial provides a precise measurement that is more directly related to the tension in the head.