“The common denominator is that we all get hungry,” says Chris Borgvansky, volunteer chef at St. Vincent de Paul’s kitchen in north Medford. Five days a week they serve free lunch to an average of 125 diners. It is a “no strings” meal, subject to only a few rules — no weapons or alcohol, you have to sit at a table while eating, be respectful to the volunteer servers, bus your own dishes, and wear appropriate clothing.