Loxx Security Lock NI

Very safe, robust, almost unbelievably easy to use and set up, and they stick out much less than any other lock system I know, which is a HUGE positive thing when you screw these locks to an ES335-type guitar.
BUT... be aware that there are two types of lower part (the part that goes on the back of the strap); one "short" and one "long": the short type has a screw thread that is only 3mm long (the long is 5mm) and it will fit only straps with very thin ends. And since this part is 10mm wide it is a real pain in the... uhm... neck to fit the lock on a rigid strap end, since the holes of strap ends are about 3mm in diameter. So, when you order this strap lock ( and you do, because they are by far THE best locks around) REMEMBER to specify which version you need, for thin or for thick straps, AND do as I have done: buy a punch cutter, 10-11mm, and make the holes on you strap ends to fit the lock.