What considerations apply to material selection for cartridge mounting bolts?

Confession - my embarrassing failure when setting up my new Holbo system.

The system needs to be quite level and there is a further adjustment on the rod which is the track for the tangential tone arm.  To make this adjustment, the tracking force has to be set to 0.1 grams at which point the arm just glides on air like a blob of mercury on a glass plate.

I have a Chinese digital scale with Chinglish instructions to measure tracking force, but I found 0.1 extremely hard to set.  Further the arm was prone to fall over backwards.

Once that was done, the real tracking force needs setting so as a test I went for 0.7 - again it was extremely hard to set exactly.  Next came my Acoustic Research Demonstration Record which starts with a Bach organ piece.  The Holbo simply could not track it.  I thought I had made a very expensive mistake, so had a cup of tea, a Bex and a good lie down, as the Aussie ad says.  Bex = headache powder.

Then it dawned on me - the scales had to be wrong and I had not bothered to use the 20-g weight to calibrate them.  Then I discovered they were set to measure in gn which I misread as gm for grams,  Now a grain is about 0.065 grams so I was attempting to track at about the weight of a bee's dick - a traditional Australian measurement.

@dover 

Tech Das are M2.6 ( Japanese standard )

Acoustical Solutions M2.5 ( euro standard )

That's the great thing about Standards.  There are so many to choose from.

Both my current cartridges need external nuts, probably because they have plastic bodies.

I think there are good sonic reasons to couple the cartridge as tightly as possible to the tone arm in order to channel vibrations away from the business end.  The fact that Rega makes a torque tool (AUS-369 mind you) supports the concept as do Wilson Benesch research papers.

At the same time, keeping the inertial mass of the business end low also makes sense.  Combine the two requirements and titanium wins of the metals.  Nobody here seems keen on nylon.  Nylon has the advantage that it is immune to eddy currents and to magnetic effects

 I was attempting to track at about the weight of a bee's dick - a traditional Australian measurement.
 

LMAO

I have a digital scale that I thought was accurate. It was off by a full gram!!!

so instead of 2gr my vtf was set to 0.9 and distortion like I’ve never heard before. 
Got a riverstone audio stylus force gauge and all is well now. 

Cartridge bolts contribute significantly to a cartridges total weight once a cartridge is mounted. Aluminum is light, immune to hysteresis and readily available. Choose only the length you need. 

You only need enough torque to permanently hold the cartridge in place once you’ve aligned it properly. You want to avoid deforming the cartridge body and the head shell from too much torque!

For VTF I’ve always used the Shure SFG II which is precise, repeatable and as accurate as it needs to be. Always at the ready since you don’t have to worry about the battery discharging when it’s been sitting unused for years at a time. The only issue is availability since it was discontinued by Shure when they abandoned their cartridge business.
 

@faustuss I really like the Riverstone Audio gauge. You should check it out.