I have Hipshot Extenders on all my basses and use them almost daily … for the few Drop D songs I play.
Love them!
Hipshot was slow to answer my requests, but @howard might say something about the size that fits a Yamaha. If you know that, it will be easy to find something fitting…
EDIT you might have 14mm holes on your Yamaha, see: Yamaha TRBX174 replacement tuning machines? - #3 by MikeC
If this is true, my Hipshot GB7 Bass Extender would fit. Note that they look a little different and require you to drill a new hole for the screw. No biggy!
There might be other ones that have the same look as your tuners and do not require drilling for the screws, like the Hipshot Ultralite Xtender HE6 Clover 3/8 Bass Tuning Machine
Note that there are two variations: one for 1/2" and one for 3/8"!
