If you need to cut a bolt to proper length, first thread the nut on, past the cut mark. After cutting, file- off sharp edges, then back the nut off to clean up the threads. To clean up rusted or damaged threads on a bolt you want to salvage, cut a slot through the side of the right-size nut. Clamp the nut halfway into a vise with the slot down, then run the bolt into the nut. For more cleaning action, tighten up the vise on the nut.
To keep tools rust-free, keep them clean and dry by wiping them off with a dry clean cloth before you put them away. To combat rust and corrosion that is caused by humidity, occasionally coat all metal surfaces with light oil. If you live in a humid climate or keep your tools in the basement, a dehumidifier will help.