Progressive, 2600, Polished Brass US3, 2-1/4" Solid Brass Door Knob Set With Spindle For Marks Surface Mount Mortise Lockset & More. For Marks Brand Type Surface Mount 91A 71A Mortise Lockset & More. Our most popular replacement knob for over 60 years. 2-1/4" diameter, supplied with case hardened set screws and a 3-1/2" straight spindle. Packed one pair per box. Standard spindle is 20 TPI.