Dexter Old style 4303 series Heavy Duty Dexter duty single cylinder deadbolt with 2-3/8 backset
This Old Style Dexter were commonly used on Steel Security Doors with small holes. Current hardware does not work.

Brand: Old Style Dexter ( NOT Dexter by Schlage)
Application: Entry Door
Backset: 2-3/8 inch(60mm)  ( commercial doors normally use 2-3/4)
Cross Bore: 1-1/2 inch minimum, designed for 1-3/4" hole
Latch Bore: 7/8 inch Minimum, designed for 7/8 - 1 inch hole
Color Finish: Polished Brass US3

Note: Old Dexter and Master are interchangeable Deadbolts, The Master had a different Latch design.