What considerations apply to material selection for cartridge mounting bolts?

@lewm 

I think this whole issue of cartridge hardware is a bit silly

I would not for a moment suggest swapping out existing bolts for $250 titanium replacements, but circumstances have forced me to get two longer bolts so I thought I'd ask the question, mindful that at one time nylon was touted as very good.

I now believe that if the cartridge has a strong metal body, it will take a lot of torque and titanium or non-magnetic stainless-steel bolts would be best.  If eddy currents matter, there will be more currents in the metal body than in the bolts.

If the cartridge has a plastic body, the lighter weight of aluminium may, literally, tip the scales that way.  The low tensile strength of aluminium becomes irrelevant if you cannot take advantage of high torque.

In passing, I note that high strength aluminium alloys like duralumin have poor corrosion properties compared to titanium and most stainless steels.

Finally, I think my cheapo Chinese digital scales are identical to branded ones at three times the price, with the exception of the Chinglish manual.  They are very easy to calibrate with the supplied 20-gram test weight.

Oh, finally finally the SME 3009 improved does not need any scales.  You just get it level then slide a small weight along a scale marked in 1/4 gram intervals.  KISS

I certainly don’t blame you for not wanting to pay $250 for cartridge hardware. I never would either. But in 3 minutes of searching on eBay I found titanium screws for under $20US. In both M2.5 and 2.6 sizes.

@lewm 

But in 3 minutes of searching on eBay I found titanium screws for under $20US. In both M2.5 and 2.6 sizes

Here's my problem.  They must be at least 18-mm long not including the bolt head. I would prefer to get washers and nuts included.  And they have to ship to Australia.

With these restrictions, over three days of searches, I have found suitable aluminium and stainless-steel bolts but no titanium ones unless you count that 50-pack which is bolts only.  The search is made more difficult because most webpages want the diameter and length to be separately selected, before proclaiming that combination is out-of-stock

Possibly radio-controlled model car outlets have them in Australia, but sod's law has me in Canberra which is a country town compared to Sydney.

As a matter of interest, I have just weighed the two bolts that are too short.  They are probably stainless-steel and come in at over 0.5 grams including nuts.  The cartridge is only 6-grams

18mm! Yes, that is a bit long but not unobtainium. I think some of the ones I bought in Tokyo are that length. I will take a look at my stash.  If I have any, I will send them on to you. Otherwise, if we can both remember for that long a period of time, I am slated to visit Tokyo again in the early spring (northern hemisphere). I know exactly where to buy them in Akihabara.

This eBay vendor has M2.5X16mm, if that length could possibly work.Here

@richardbrand  on mounting problems

The SME 3009 improved and Shure V15 mk3 was right up my street in the 70s, along with the Garrard 401 and SME plinth system. The whole rig was quite the standard go to front end. I found the V15 mk2 was more forgiving with vinyl imperfections.

SME offered as an upgrade at the time, nylon nuts and bolts to cut down mass just after the “improved” arm launch. I went down that road which was against the bolt everything up as tight as possible norm. I never noticed a difference to be honest. 
 

I tried recently to put my V15 mk3 back into service and had the same problem with needing longer bolts. The cartridge is not very strong laterally as metallic nuts and bolts can distort the shell as washers larger than the bolts don’t fit. There’s no spare diameter to ensure a more secure fix. The nuts can slip sideways (as not captive) out of the mount. The plastic is then compromised forever.
 

l never thought the cartridge worked anywhere near spec using compatible after market styli. The Shure “trackability” was just not there. The new stylus would not track their test record at the highest modulations like before.

Good luck with your quest to get this classic cartridge up and working again. My cartridge ended going back into stock. After l first retired the V15, l started using a Goldring G900IGC that runs to this day, having a spare NOS stylus in reserve..