I wanted to use 10-speed Campagnolo components on a couple of road frames I have that are 135mm rear spacing. Problem is that Campagnolo only make their rear hubs in 130mm spacing. I could have used Shimano compatible wheels and Shimano cassettes modified by Wheels Manufacturing to use with Campagnolo 10-speed derailleurs and shifters, but those cassettes are a) very expensive and b) they bring the derailleur very close to the spokes - close enough to be unusable with some hubs. However, Campagnolo Record rear hubs use a detachable nut on the end of the non-drive side of the axle (part #FH-RE127 in the Campagnolo catalogue), and as I have access to a lathe I decided it wouldn't be too difficult to make a 5mm longer replacement nut. In case you're wondering, there isn't enough thread on the Campagnolo nut to simply add a 5mm spacer between it and the axle. About 1-2mm would be the maximum that you could gain with that approach.
My first port of call was a couple of local engineering supply shops that specialize in fasteners, to see if I could find any bolts using the same thread, with a view to somehow modifying a bolt to do the job. Doing this would at least save me from having to cut a thread. However, they both got out their thread gauges and calipers, measured the Campagnolo nut, and told me that it didn't correspond to any available imperial or metric thread bolt. This left me with having to make the nut from scratch if I wanted to pursue the modification.
I then thought of using stainless steel for the replacement nut, but as I was going to have to cut my own thread on the nut and also wanted to broach it internally for a 5mm allen key in the same way as the original, I decided that brass would be much easier to machine and adequately strong for the purpose. I also happened to have brass stock of a suitable size already on hand.
Campagnolo's original nut on the left, three of my 5mm longer brass copies
As it turned out, the job wasn't difficult, merely tedious. I eventually made four of the caps, as most of the time it took (about eight hours in all, including measurement of the existing nut first and cleanup of the lathe afterwards) was in the setting up of the lathe for the various operations, and making four nuts didn't take much longer than making one. The broaching of the nuts to take a 5mm allen key was done by first drilling a 5mm hole, then cutting off the right-angle end of an allen key to get a 5mm hex shaft, sharpening the cut end, and then using a hammer to drive the shaft through the nut in a jig. As both the frames in which I intend to use the modified hubs have vertical dropouts, I didn't bother putting any knurling on the face that bears against the dropout.
Replacement nut fitted to a Record hub