 Nearly as important as solder type is solder thickness. If it's too thick, you'll have trouble with tight spots and small devices. If it's too thin, you'll have to keep feeding solder into the joint, heating the pads longer and possibly damaging the board or part. So which size is right for the job? Delicate surface mount components are best soldered with thinner gauge, generally around .02 or .015 inch. It's like the angel hair pasta of solder, except shiny and very toxic. For through-hole soldering, .031 diameter will do the job well. Your soldering will go quickly and there's plenty of flux inside to give you good, clean solder joints. For large components, you can go up to .062 inch. But if you get thick solder, just make sure it's the electronics type and not plumbing solder.