Well you have 2 measurements when installing a new shift cable. Barrel to eye is 6 in and the other is post to post should be 3 in. Sonning the barrel is not how you should adjust shift cable. There is a small crecent shaped groove with a 5/16 but that you adjust your shift with. Loosen nut just enough so that you can change the position slightly inside the groove and snug it up and check the shift( in the water under load) untill you find the sweet spot for forward and reverse.