I purchased two sets of 1st generation F Tuners tuners from ebay.
One set were from a 1966 telecaster and although pretty dirty and one tuner basically shot, the other 5 were in great condition.
The second set was from a 1968 Telecaster. These were all in excellent condition and it was from them that I chose the tuner to use to replace the non correct tuner on the restoration project.
However when I came to fit the (1968) F tuner it just didn't seem to fit properly. The tuner in question was meant to fit in the B string location, but no matter how much I pushed it just wouldn't slot in. I removed the adjoining tuners and started with the replacement tuner and then tried to re fit the adjoining originals. This time they wouldn't fit in.
I went back to the other 5 tuners of the 1968 set and each of them also would not fit.
I then went to the 5 good tuners from the other set I had purchased (these are from a 1966 Telecaster) and each of those 5 tuners fitted perfectly. I cleaned up one of them and fitted it to the neck.
Then when I had a spare moment I compared each of the 1966 and 1968 1st generation F tuners. The 1968 F tuners have a longer turning knob shaft and my initial thought was that they must be wider than the 1966 tuners as this was the only possible explanation (I thought). However as you can see in the photos and the data below, I now do not think they are wider, but infact the variation is either (i) because the die/tool being used to stamp the other shell had deteriorated and was stamping modified outers or more likely (ii) a different die/tool was used for the stamping which, although produced units that although looked extremely like the earlier ones, they were infact different.
Width of outer cowling (of the parallelogram)
1966: 22.52mm
1968: 22.54mm
Height of outer cowling (of the parallelogram)
1966: 19.13mm
1968: 19.15mm
Width of the pressed "D" shaped section of outer cowling
1966: 20.20mm
1968: 20.45mm
width (diameter) of knob shaft
1966: 3.55mm
1968: 3.50mm
Visible length of knob shaft
1966: 9.80mm
1968: 11.42mm
Then I looked at the two sets of F tuners and started to see that the actual angles of the parallelogram shape which made up the out cowling of the tuners appears ever so slightly different.
As shown in the following photo, after measuring (roughly) the smaller angle of the parallelogram of each of the 1966 and 1968 F tuners I come up with:
Smaller angle of the outer cowling parallelogram
(these angles are rough, but even with the uncertainty there is a definite variation between the 1966 and 1968 F tuners)
1966: 70.25 degrees
1968: 69.50 degrees
As shown in the photos where the tuners are laid flat and then moved so that they are touching, the top section touches but the bottom does not and a gap between them is evident. This now explains why the only way I could get the 1968 F tuner to fit in with the other 5 1966 F tuners was to slightly rotate the 1968 F tuner. This caused the top and bottom to no longer be in line with the tops and bottoms of the other 5 tuners, as well as the screw holes to no longer match up.
To confirm this, I removed a 1st generation F tuner from my mint 1966 Jaguar and was able to successfully fit this into the B string position on the neck I was restoring.
While the above observations are only based on 4 sets of 1st generation F tuners, when one is restoring a mid to late 60s fender with F tuners, you may need to obtain F tuners from the same year, otherwise you run the risk of them not fitting correctly.
