Any time I see some rusty steel the first thought that comes to mind is "need to Boil that". Huh, why would you boil rusty steel. It's because it causes a very simple chemical reaction that changes Ferrous Oxide into Ferric Oxide. What the heck is Ferric Oxide? Ahah, that is also known as Black Oxide, the original rust preventative for steel. BTW, Black Oxide has a lattice structure sort of like a microscopic sponge, so the trick with this coating is to keep the lattice filled with Oil. It just happens that Water Displacing Oil - Formula 40 is absolutely superb for filling Black Oxide Lattices because it was originally designed for this application. Odds are good you have some on hand, because it's more modern name is WD-40.
For your current studs what you really want to do is to properly Black Oxide them. The process for doing this is known as Rust Bluing because it was originally used to protect Shotgun barrels. It's actually easy to do but it is a bit time consuming.
Step 1) Clean throughly to insure there is not even a tiny trace of oil or grease on the parts. Start with a light wire brushing to knock off the scale. Then soap and water with a scrub brush. Then a scrub with Isopropol Alcohol (or Methanol, they are the same). Then a dip in Acetone. Then dry and set them out. If a dusting of red rust appears regard that as a good thing.
Step 2) Etch the steel with Hydrochloric Acid. It's really easy to make this using products common in most homes. Those products are Hydrogen Peroxide, White Vinegar, and table Salt. The formula is simple. One cup of peroxide. one tablespoon of Vinegar, and one Teaspoon of Salt. Mix them all together and stir until you don't see any salt crystals. Note salt added to vinegar makes the Hydrochloric Acid, the Peroxide is an accelerator. Place the parts in this solution and you will see bubbles forming at the surface of the part, that is the acid at work. If you see less bubbling after using the solution for a while it means it's time to make up a new batch. BTW, this solution will also clean the tarnish off brass really quickly. Leave the parts bubbling until they look gray.
Step 3) Rust the parts by blotting them dry and setting them on a mesh screen over a small pan of simmering water. If it really humid outside just set them out. The goal is an even film of red rust that looks like dust. BTW, first few times it will probsably be sort of spotty but more rusting cycles will even that out.
Step 4) Boil the parts. Try not to knock any red rust off so steel tweezers or needle nose plyers are a good tool for handling. Boil about 10 minutes or so until all you see is Black.
Step 5) Set the parts aside to cool to 90 degrees or less.
Step 6) Put on some latex gloves and use a fine wire bronze brush to "Card" the parts. Basically what you are doing is cleaning off the loose powder from the underlying latice. Stop carding as soon as you see just a hint of gray showing. If you scrub too much or too hard you'll remove most of the Black.
Step 7) Go to step 2 and repeat. 12 to 20 cycles will get you a pretty good thickness. Hey, I wasn't kidding when I said it was a time consuming process.
On the plus side more cycles means a slightly thicker and harder surface. I'll also note that you will end up with a satin finish. Once completed soak everything with WD-40, let it stand a day or two, and then wipe it to a dry appearance. I'll also note that Oxides of Metals are actually Ceramics and some are extremely hard. Aluminum Oxide is so hard it's been used in sandpaper for as long as sandpaper has existed. Ferric Oxcide isn't quite that hard but it is a durable surface and near ideal for
wheel studs, just keep them greased and rust won't be a problem.