Drill Rod
The under size wire you are referring to is listed in McMaster's product index as "drill rod". The name refers to the actual size of the wire according to the AWG (American Wire Gauge) index, and not to their hardness or brittleness. The same sizing as in your 1-60 drill index - so you can "jump" up or down in size just a few thousanths at a time to either loosen/tighten a hinge joint. Be aware that this material is softer (read - more pliable/ ductile) than the "as delivered" pin, but I have been using them for more than 25yrs and 2500+ of RV service and have never had one fail. (If you have a real tight fit - DON'T spin them in with a drill motor! Bad juju - if you put enough torsional stress on them and they "twist" into two pieces, you now have a permanent joint!)
Although McMaster normally sells them in 3' lengths, they are actually manufactured in 12' lengths and cut down for McMaster for their convenience for shipping, etc. You can special order them in any length you want - for a slight additional cost. I got a bunch cut into 4' lengths for my Rocket cowl back in the late '90's and still have an "inventory" that I use as needed.
The typical pin as received with the hinge is on the order of .089" - drill rod (as I recall - I am not home now, so this if from memory) is available in .088, .085 and so on down the line. Somewhere in there should be a size that will help. Use the "loosest" fit that works for you, and then over time as the hinge eyes wear a bit you can jump up a size (or more) to "tighten" the joint again to your satisfaction.
YMMV
HFS
