My parents were in town this weekend to help with the baby, but my dad's way of helping was to knock things off my to-do list that were looking to be, in the near term at least, impossible. Like patching some rotting boards on the back deck. Because those boards are mounted at an angle, he needed a sliding t-bevel to reproduce that angle, and I offered to lend him mine. It's a pretty basic Stanley t-bevel. But he couldn't get it to work well, so he went back to using his own, which is also a Stanley t-bevel, but a bit older.
There's a clear difference. The new Stanley has a knob up at the top you turn to tighten things down, where as the old one has a thumbscrew at the end. The practical difference is that it's nearly impossible to tighten the new style without changing the angle at least a little, whereas that's easy as pie with the antique one.
Overcome with feelings of inadequacy, I went looking online for a replacement, but damn near every t-bevel I found had the same flaw as my newer Stanley. I did find a Japanese-made one that has the same kind of thumbscrew as the antique, and it's less than $20, which isn't too bad, I guess. Of course, then I found this one, and the $20 seems kind of clunky by comparison. But I can't quite bring myself to blow $50 on a tool I so rarely use.
Thankfully, there's still eBay, which seems to have several reasonably priced antique Stanley t-bevels.