Inspect jars for cracks, chips, or scratches. Wash jars, lids, and rings with warm, soapy water. Place jars and lids in saucepan filled with simmering water and retain heat until ready to use.
Peel, pit, and finely chop peaches. To peel, submerge in boiling water for 60-90 seconds and dunk in a sink full of cold water. Slip the skins off with your fingers.
Place peaches, pectin, margarine, and lemon juice in a stockpot. Bring to a boil. Add sugar and boil hard for one minute, stirring constantly. Skim foam if necessary (the margarine reduces foam occurrence, so don’t worry if you have none).
Ladle into hot jars, leaving a ¼” headspace. Wipe rims of jars with a damp cloth and affix warm lids. Tighten rings.
Place in water bath canner and bring to a boil. Process for 10 minutes.
Remove jars from canner and allow to cool on a towel. Check the seals after 8 hours. If the lids still have some spring, reprocess or refrigerate for immediate use.