I have Shimano 600 calipers on my bike and when I got it I noticed the adjuster threads seemed stripped. They still worked okay but I decided I was going to replace them due to it. I took the front caliper off to measure it for a replacement and upon doing this I noticed that there never were threads int he caliper itself. Instead, it had a plastic insert when new but that was mostly missing. Is this a replaceable item or am I going to have to make something to take its place? If its to difficult (or expensive) I'll go with my original plan to replace the calipers.

So just to answer this for posterities sake, these are not available if anyone else runs into the same problem. I checked with my LBS and they had nothing that would work. So I am going to look at making one out of brass or aluminum provided its not some crazy thread size.

Yer talking about the main cable adjuster — not some grub screw thingy for synchronizing dual action pivoting calipers — right? Either way, I hope that post a pic of any fix because I own sets of 600/Utegra and cousin brake sets. Good luck!

Yes, the cable adjuster threads into what looks like was a plastic threaded bushing of some sort. I'm guessing it was injection molded in place as there was the remains of a locating pin that was pretty stiff, though over the years I guess it could have hardened. I'll post results when I have them. I'd hate to toss these as they are pretty much perfect except for this bushing thing.