For those of you shooting smaller diameter carbons like the Carbon Express Heritage 75 & 90 or the CE Predator II 20/40 there are no brass inserts currently manufactured that fit those shafts. However it is very easy to mill down standard size brass inserts with tools you probably have laying around.
Get yourself a drill (with a trigger lock), some bar or C-clamps, a single cut mill bastard file, a triangular file and some safety glasses. Clamp the drill on its side to a stable surface like a workbench or table. I used two bar clamps to hold the drill down to the tabletop. The drill should be spinning towards you. Screw a field point into an insert. Place the field point into the drill chuck and torque it down. Fire up the drill and lock the trigger. Now all you need to do is apply medium pressure to the file on the brass and work the file back and forth until the proper diameter is achieved. I checked for fit with one of my arrow shafts. Once proper diameter is reached I used the triangular file to cut three grooves around the insert that give the glue something to bite into.
I was able to take a dozen 100 grain brass inserts down in about 30 minutes. I ended up with 85 grain inserts that perfectly fit my shafts. Love my homemade metal lathe.
For the record I didn't come up with this method. I read about it on this cool forum called TradGang. I was nervous about trying it out, but it is really simple and allows us skinny lightweights to add some nice mass up front. Good luck.