My hands are on the small side, but these keys are big. The sale I got these from is just down the road from several prisons tho. Prison key is a possibility.
Folger Adam Company purchases the detention lock lines of Sargent & Greenleaf and Yale & Towne. Folger Adam Company later purchases the detention lock line of Stewart Iron Works. They are the only manufacturer of both mechanical and electromechanical locks for prisons until 1967.