I installed the bushing provided with a pivot hole around 3.5mm, then drilled it out to 10mm as specified. The hole should be centered precisely in the middle of the internal bore of the barrel—not the outside middle of the barrel, as clearly explained in the supplied instructions.
I let the bushing sit just slightly inside the bore, with minimal intrusion. Be sure your barrel of choice isn’t too wide on the outside—leave a bit of clearance outside so the mic unit fits properly later on. Once the epoxy cured (to be safe after 24 hours), I tested for any leak and found none. The fit was perfect—truly a plug-and-play setup.
The pickup produces great sound overall and you don't need a treated room, literally can play in any space. There is a marginal key noise when playing quietly and this can be used as an effect, too.
If you plan to use the pick-up with guitar pedals and so on, make sure to buy the PK-K1 cable separately, as it’s not included in the kit.
Very happy with this purchase—installation was straightforward with the right tools and care, and the sound performance is excellent.
