I have a 1986 F250 witch i use as a tow rig and the ring and pinion is bad now. The question is all the listings that i have found are for a 10.25 ring and mine measures 10.5. Is it that I'm measuring wrong or is there a 10.5 ring and pinion out there?

check for the axle codes, maybe on the pumpkin there is a tagor or the drivers door there should be a axle id code on the sticker. With that code you can tell whats in there.
JFR-