I don’t use 2/56 for anything. Solid carbon fibre rod of the same diameter is stiffer, stronger and lighter so if I have need of small lightweight control rod carbon is my go to.

I use 4/40 and up depending on size and force needed. Again the bulk of the control rod for anything over 10/12 inch’s is carbon fibre tube that just fits over the end pieces of 4/40 rod. I try and keep the 4/40 rod as short as possible. The 4/40 rod I like are the packages of threaded double ended rod in various lengths. For the adjusting end I pick the length of rod that allows one threaded end to slide inside the carbon rod and the other end out for the clevis of your choice. Rather than grind or try and form notches in the end you are epoxying inside the carbon rod the other threaded end will do a much better job at creating a solid anchor.

For the other end that I am going to solder the clevis I cut one of the longer double enders or use a single threaded end rod and insert the threaded part with epoxy inside the carbon rod. I leave the unthreaded end a little long to be fitted at assembly.

If you use actual 4/40 rod for this you will find the clevis will have to be turned on to the rod and should hold its position during soldering. Position the clevis on the threaded rod so there is enough exposed thread inside and outside the clevis to allow for adjustment both directions and attach to one end of the connection preferably where you need/want to do any adjustments.

Servo arm is centered and a locking nut is in place on the pushrod behind the clevis. I lock the control surface centered by using a bit of balsa strip top and bottom and held in place with two close pins or light weight spring clamps.

You can attach or push the clevis pin into the control horn and lift the rod to align with the clevis, mark and cut to length. A clevis such as the Sullivan should have 1/8 of the steel pushrod exposed inside the clevis. Because the clevis is so snug a fit on the 4/40 rod any solder on this exposed part will not allow the rod no mater what to pull through even if your solder joint should fail.

Sand/clean the rod and use a little acid flux on both the rod and clevis then wind into place checking for length by again aligning the clevis pin with the hole in the control horn. When you have it right just let the whole thing hang free and apply a bit more acid flux and solder in place. Any slight misalignment that occurs is easily adjusted at the other end.

Since the flux is acid I mix a slurry solution of baking soda and brush on the solder joint then clean with soap and water.

I prefer Stay bright only because of the convenience any other solder will do the job just fine. The Stay bright joint always looks nicer.

Dennis