What is the center-to-center spacing of the 8 knockouts in the jamb shield, and what are the measurements of each rectangular knockout hole?

The center holes on the Jamb Shield are 3-1/2 inches apart. Each of the holes on the Jamb Shield is 2 inches long. The Jamb Shield will fit locks spaced from 4-1/2 inches to 21-1/2 inches apart. In the event, your locks don't fit (which does not happen often), it is fine to file out a 1/8 to 1/4-inch to make it work. That will not void your warranty or cause any other issues. We use galvanealled steel so rusting is not an issue. Did this answer your questions? Thank you for your feedback