Here's the skinny on the rebolting of Feather Canyon that Clint and I did. As near as I can tell, all bolts placed by the FA party were a 1/2" diameter stud with internal threads that accepts a 3/8" threaded bolt. As you tighten the bolt you push a pin to the back the stud which expands and provided holding power . It is really hard to replace this type of bolt without causing a huge crater so we unscrewed the bolt, removed the hanger and left the stud in place and patched over it.
It is interesting to note that when we unscrewed these bolts many had been cut to shorten them probably indicating that the bolt tightened up before it was flush with the stud.
All bolts we placed were 3.5"x3/8" SS Rawl(Powers) 5-piece bolts and Petzl Couer hangers.
Pitch 1: on the FA, no bolts were placed at the belay. Sometime, probably in the 90's someone added a single, 3/8" non-SS wedge bolt. More recently, someone took the hanger off that bolt and added two non-SS Rawl(Powers) 5-piece bolts and Fixe single ring hangers to the belay. We didn't touch anything here.
Pitch 2: recently, someone added two non-SS Rawl(Powers) 5-piece bolts. One bolt has a Fixe single ring hanger the other bolt has a 'standard' Fixe hanger. We didn't touch anything here.
Pitch 3: The first bolt you reach was added after the FA. It was a 3/8" Star Dryvin that was improperly placed(only the nail on the outside of the hanger. We replaced it. The second bolt was placed during the FA. We replaced it. The third bolt was a 3/8" wedge bolt, probably added in the 90's. All the rock around the bolt was hollow. Replacing it would have required moving it 6-8 feet and since it was not placed by the FA I left it, but did swap the Leeper hanger for a Petzl. The fourth bolt was placed by the FA so it was replaced.
Pitch 4: the first bolt was a 1/4" Rawl split shaft. It was probably not placed by the FA, but it has been there for a long time and it protects the crux so we replaced it. My guess is that the tree there was a bit higher BITD so that bolt wasn't necessary on the FA. The second bolt was placed by the FA so it was replaced. Next were two studs with no bolts. It is not clear why there were just studs. Most likely the FA party had bolts in them and but were removed maybe because they were running out of hardware higher up. We screwed 3/8" bolts(taken from the previous pitch) into those studs and put Petzl Couer hangers on them. The bolt at the top of the pitch was replaced. That makes five bolts on the crux pitch. Three are SS and the middle two are not.
Pitch 5: We replaced the two bolts placed by the FA party. Clint found a hangerless stud between the two bolts, most likely placed by the FA, and decided to replace it with a SS Powers bolt. That makes three bolts on this pitch.
Pitch 6: no bolts on this pitch(which was good since it was dark by the time we got there on our first attempt to rebolt the route).
Pitch 7: we replaced the single protection bolt. The belay bolt was a 3/8" Star Dryvin which was probably not placed by the FA (it had a SS SMC hanger on it all other SMC hangers on this route were the old, thin, plated variety), but we replaced it anyway as it seemed like a good idea.
Pitch 8: we replaced all three protection bolts on this pitch even though the third bolt was a 3/8" Star Dryvin with a Longware hanger and most likely not placed by the FA. We also replaced the two belay bolts on top of the pitch - the 2nd summit of H&L. One bolt was a 1/4" Rawl split shaft. The other was a very old Star Dryvin bolt most likely placed by Dick Houston and Fritz Lippmann on the FA of H&L in the 40's. It came out very easily!