I am very happy with these Tuners. There are no instructions included in the box, but they are super simple to install on an American Stratocaster. Once the old Tuners are off your guitar, just align the two small nodules on the underside of the Schallers with the old screw holes and they fit perfectly. Took me just a couple of minutes to get them on the guitar, insert the new strings and lock them. Couldn't be easier - but remember these are staggered - so you just have to be sure that you install the 3 longer ones in the 6th, 5th and 4th positions !
These are a great product. Very well built, great quality, rock solid. I'm glad I invested in them and for the first time in my life I'm actually looking forard to restringing the guitar !!
So, if you're thinking about it, just do it ! Money well spent as far as I'm concerned.