I couldn't find this information anywhere, so I'm posting it case it helps anyone in the future:
I wanted to replace a cracked nut on my 1977 Guild F512 with a pre-cut nut, and went in search of one. After a lot of searching for guidance, I found a GraphTech sizing chart (http://moridaira.jp/wp-content/uploads/2013/10/9f4918492706d08043b8c27a6bd53949.pdf) that recommended the PQ1578. I got it installed and while it felt a bit different from the nut I was replacing. More importantly, wherever I tried a capo, the low E strings could not be fretted cleanly. I contacted Graphtech, who maintained that the 1578 was the correct nut.
Last night I tried the PQ1568, with the slightly smaller E to E measurement. Works much better - I love my 512 again!
I wanted to replace a cracked nut on my 1977 Guild F512 with a pre-cut nut, and went in search of one. After a lot of searching for guidance, I found a GraphTech sizing chart (http://moridaira.jp/wp-content/uploads/2013/10/9f4918492706d08043b8c27a6bd53949.pdf) that recommended the PQ1578. I got it installed and while it felt a bit different from the nut I was replacing. More importantly, wherever I tried a capo, the low E strings could not be fretted cleanly. I contacted Graphtech, who maintained that the 1578 was the correct nut.
Last night I tried the PQ1568, with the slightly smaller E to E measurement. Works much better - I love my 512 again!