Hi,
A diamond tip last's many stones lifetime if the user is careful. The model shown in the pictures was made before we had the adjustable nut on the support-bar as standard and I can see that it might have worn down faster than the set-up we have today with the TT-50 and US-105 with micro adjuster. It was more difficult to set it at a specific height.
They wear down faster when you remove a thick layer of stone. Then the stone wears down the copper from the side and the diamond will loosen faster. When I use a TT-50 I mostly set it around 1/2 step and rather go faster over the stone several times, and finish with the stone grader on its course side to smooth it out. Then the surface looks like a new stone too.
Luckily, I learn new things about our product too on a regular basis and I was told that diamonds can be up to 5mm in the tip, so more than we have learned in this tread.
Best,
Stig