Schaller S-Locks M NI

On the whole these are better than the old Schaller strap locks: the attachment to the strap is much easier to do and there is a grub screw which means that once you've got everything right and tightened it up on the strap then it will stay that way (you need a fairly fine flatbladed screwdriver for this, but you don't need to do it up).

But there is a critical design problem. The strap buttons themselves are now integral with the screws that go into the guitar (this was not the case for the older locks), and these screws may be larger than the existing ones. If that's the case for your guitar then screwing the buttons into the guitar will widen the holes in the guitar and mean you can never put the old buttons back. Worse, it could possibly split the wood of the guitar which would be very bad (it did not for me).

So I would look for an older set of buttons if possible.