This is a custom cap I made for my guitar projects. I used it on my PRS Style guitar, as well as on my LP Style guitar. I realy like this shape and due to the slightly flat sides, you can line it up with the switch direction, so even without a Name Plate/Washer like on a LP Style gutiar, you can tell, where to press the switch. The hole is 3.4mm. You may have to drill it slightle bigger, or make a bevel, so the thread of the switch can grab the plastic and cut it. I haven´t done that to the part, to have a bigger surface for printing.