The buildings and the hardware
The buildings here tend to affect the hardware we use. Older houses often have hollow-core doors, narrow stile molding, and mortise or surface-mounted latches that need different plates and screws than modern frames. Many multiunit buildings use apartment-grade cylindrical locks on interior doors and heavier commercial-grade exit devices on storefronts; that changes the parts we carry and the fasteners we fit. A lot of original oak doors have narrower rails and require longer screws or reinforced strike plates to hold a deadbolt securely. Knowing the door and frame construction means we choose the proper latch, bolt length, and reinforcement material on the spot.