This is a standard 5.75 inch (145mm) avionics slot panel that fits the ACK Technologies ELT (Emergency Locater Transmitter) cockpit remote E-04.5.

Recommend printing in ASA/ABS or other high heat tolerance material as this will be in a potentially hot aircraft sitting outside.

I have two versions, one will fill 3 spaces, or 1.1 inch (28mm)

The second is 1.5 inch (38mm)

Items 

4 M3 X 6 X 4.2 heat set inserts

4 M3x6 screws

For quarter turn mount you will need two each of D5-PFSC35-38A-190 Dzus fasteners.