Did you try Google?
I just looked at photos of both arms. The TP90 arm photos all showed conventional looking cartridge mounts on what looked like standard plug-in type headshells. The TP16 arm turned out to be the arm I recently installed a cartridge in. I think you have the TP16. You have to screw upward into the sliding metal shim-looking plate. It has threaded mounting holes but you have to have screws of just the right length for your cartridge. My problem was that in my case the little plate had corroded and you couldn't hardly see the corrosion filled mounting holes. I was able to make it work, kind of.
Thanks for the replys.
I looked through photos of various arms. What I have is a two piece arm. The arm part with the headshell on it says Thorens. It looks like a TP63 or TP70 arm that I,ve seen in photos. The photos of the Tp16 I've seen show a large headshell. Apparantly Thorens would take the same tonearm, change the headshell and use a different tonearm number. I did not see any photos of the headshell on my arm which is connected to a 5" length of arm tube.
I am thinking of buying a headshell/arm combination for TP 63 0R 70 plug it into the other arm section. Based on photos they have a fairly standard cartridge mount.
Last resort is to modify the tonearm I have. Drill holes etc. but don't know if that is sacreligious. It's a bit above my level of expertise.