Men who are single who have participated before in the SBO must be upholding the general characteristics listed in the qualifications for a Deacon and have a plan for personal daily Bible study and prayer time. Their Pastor should confirm this in their reference letter.
I Timothy 3:8-10
8 Deacons likewise must be men of dignity, not double-tongued, or addicted to much wine or fond of sordid gain, 9 but holding to the mystery of the faith with a clear conscience. 10 These men must also first be tested; then let them serve as deacons if they are beyond reproach. I Timothy 3:8-10.