Cut out of 1.2mm sandblasted stainless steel or 1.2mm black Delrin (POM).
Steel plates are available in two layouts, AT101 and DCS, with versions for both Frog variants (F12 WK and F13 WKL). POM plates are available in variable layouts for both F12 and F13. These variable layouts will fit almost all ANSI keycaps, with tear-offs to convert the Alps stabilizer holes into MX stabilizer holes.
Alps switches are a tight fit in this case, so a barrier (such as electrical tape) between the switches and the case bottom is necessary to prevent shorts. If additional clearance is desired, 1 x 2.5mm o-rings should be added between the plate and bottom of the tadpole.
Note: Due to the flexibility of POM, it is highly recommended to cut 1mm off the bottom of the switch pins after soldering to avoid bottom outs.