Originally Posted by ken snyder
.0005 test indicator for run out. They're just easier to see whats going on is all. More important is a good base to put it on. Tenths is mainly spoken as a tolerance around a number ending in a thousandths - just a language for a tolerance around the last significant decimal place. If the last decimal place is a tenth then the tolerances will be spoken as hundredths (.00001) - Barrels are a Mystery judging by all the different sized pilots available for each caliber.
slightly off subject, but regarding dial indicators if it matters a lot. I said earlier that I use a lot of Interrapids, and most folks think of them as the Roll Royce of dial indicators (I've seen one that's better). The onething I hate about a dial indicator is when you adjust the dial face (turn it) is that most will move all over the place. That .0005" Interapid stays put everytime. Now I have one of their .0001" ones, and hate it! It's just too sensitive to movement. But when I had to be right on the money it was dragged out of the box. The Federals are pretty good, but their dials are too stiff for adjusting in my book.
A good rule of the thumb is that if you want to work within .001", it's best to use a .0005" indicator that has fairly good travel (.025" is plenty enough). I even had a couple .000050" Federals I used for splitting tenths when building gauges, and I often commentted that they were pretty much a joke to use! Still it made other folks happy. Also keep in mind that 80% of the dial indicators sold do not like to be set at the 12 oclock position, and then be turned upside down (6 oclock). The only ones you can do that with are the Interrapids and the B&S Best Test