I've never used them or needed to. My Strats a 72 with a 3 bolt neck and rarely goes out of tune. I use the whammy bar quite a bit too. If the nut is cut correctly and you use a little lube on the friction points, and the guitar is set up correctly with the strings properly stretched, you should not have tuning problems.

Same here, my 70's Strat hold tuning fine even with tremolo use. Except sometime the first few days after putting new strings on.

I have a MIA 1989 strat plus w/ Schallers and a couple other sets of Sperzels. They are both equally good except that the part you turn to lock the strink on a Schaller can come off whereas the one on a Sperzel will not. I have seen used guitars in stores almost always missing one of the locking pieces. Take it for what it's worth.

thanks to everyone for your help, i found locking tuners that will fit without drilling. These are the Goth Vintage Locking tuners. Again thanks for all the suggestions and comments