additional secondary trainingFollow

I have tinkering and transmuting secondary skills. I seem to hit a wall in transmuting at 100. I have broken down a lot of items and no skill increase. The stat is 100/175, so I'm assuming skill increases until 175. What happens after 175? Go back to Butcherblock for more training or what? I note that tinkering caps at 375. Are the icons used for tinkering good all the way through 375, or can you get more powerful icons like in regular tradeskills? Thanks.