So let's say you have just finished testing your newly assembled couplers. You have one that won't work, and you have determined that it will have to come apart. No big deal. Set the coupler (upside-down) in a jar of acetone for about 15 minutes. Leave the jar covered because this stuff smells. Acetone is available at hardware stores and even in the paint department at WalMart. If the smell seems familiar, it's because acetone is the main ingredient in fingernail polish remover. Don't use polish remover though because it has typically has moisturizers added which we definitely don't need gumming up the works.

After waiting 15 minutes, pull the coupler out of the acetone with tweezers. Pull the bottom and top castings apart. You might have to grip the bottom casting with needle nose pliers to separate it. While the top casting is still wet with acetone, tap it on a table top to encourage the ball to fall out. Be careful not to damage the paint on the coupler because the acetone may have softened it considerably. The picture here shows a top casting as right after it was removed from the acetone jar. All the paint is bubbled up and looks horrible. Have no fear. Leave it alone for a few minutes and the paint will recover and be nearly as good as new! Experience with your brand of paint may vary.

The acetone will evaporate quickly. Some partially dissolved glue may be left on the castings, but that's usually not much of a problem. Once it evaporates you can go to work diagnosing the problem.

It seems all the troublesome couplers have something different that makes them troublesome. For this particular coupler I could drop the ball into the cylinder then turn the top casting over and the ball just didn't want to fall out. No amount of burnishing with the toothpick end seemed to help. Finally, I chucked a #59 drill in a pinvise so its shank was exposed (not the hole cutting end of the drill). I spun that in the cylinder a little and the problem went away.

The rebuilt coupler works like a champ now.