From Dimarzio website: dimarzio.com/faq#55/65/7568
"F-spacing refers to the wider of the two spacings. For proper string alignment and balanced output, F-spaced humbuckers should be used in the bridge position on all guitars with string spacing at the bridge of 2.1" (53 mm) or greater. On these guitars, if the nut width is 1-11/16Ē (43 mm) or greater, F-spaced pickups can be used in the neck position as well."
The JS1200 has the JS
Prestige neck with a 42mm nut so LonePhantom is correct. F-spaced for bridge and regular for the neck.
Furthermore, beyond the 'marketing fluff', the reason for the two spacings (from Dimarzio) "A long time ago (in the 20th century, actually) the electric guitar world was divided between Gibson and Fender designs. One of the differences between the two was string spacing. In general, Gibson chose a narrower string spacing at the bridge than Fender, and therefore the polepieces on Gibson humbuckers were closer together than the magnets on Fender pickups. When guitar shops started installing humbuckers in the bridge position of Strats, it was obvious that the strings didnít line up with the polepieces, and if the E strings were too far outside, the sound could suffer. Our first humbuckers followed the original Gibson spacing, and we call them standard-spaced. When we released our first humbuckers with wider spacing, Floyd Rose bridges were very popular. Floyd string-spacing is the same as Fender spacing, so we naturally called the new pickups F-spaced."