Since this is a PEGHED posting, I should not get flamed for mentioning where you can get your PEGHEDS at the best price, and a selection you cannot get anywhere else.
I have them with a 27.5mm shaft and a 19mm shaft. With a 12mm peghead/headstock, the 27.5mm sticks out the back 15.5mm. With a 19mm shaft, it will only stick out7mm. What do you do if your hole is larger than 7.5mm? Shim the hole or plug and rebore....or get an 8.5mm or a 9.5mm diameter shaft. What if you want a chrome unit rather than basic black? It has an ivoroid button that really is nice. [When my XP crashed, the material switched over to my 8.1 did not include my web site www.pegheds.net---my computer whiz-bang is back from Afghanistan, and we will get it up and running again this month] My price for the basic black set is $56.00 a set of four. That means they are $14.00 each. Want 3L3R? do the math. Want ' em all to turn the same way because you have a diagonal pattern instead of 2L and 2R? no problem I also have them for banjos and guitars--- but they cost a little more. Priority mail within the USA is $6. Out of the USA costs more. Cash- check- PayPal....you get dinged for the P/P fee.