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What size hole is required for most door knob sets?

  1. 2 1/8"

  2. 1 3/4"

  3. 2"

  4. 3"

The correct answer is: 2 1/8"

The correct choice is 2 1/8", which is the standard size hole needed for most door knob sets. This measurement ensures that the cylindrical locks, commonly used in residential and commercial settings, can be properly installed. Using a hole of this size allows enough space for both the knob mechanism and any accompanying hardware to fit securely within the door without compromising the integrity or function of the door itself. The other sizes listed do not conform to the standard for door knob installation. A hole measuring 1 3/4" is typically associated with the thickness of the door rather than the hole diameter needed for the knob itself. The 2" size, while close, does not adequately accommodate the components of standard door knobs, potentially causing installation issues. A 3" hole is excessively large, leading to structural problems in the door and making it difficult to properly secure the knob and latch mechanism. Therefore, 2 1/8" is recognized as the optimal and most widely accepted size for this purpose.