Note: This is directly derived from @mitxela's Morse USB Keyboard Mk II; this varies from his design only in that it includes minor hardware changes and slightly altered software. If you were interested in this project, you will probably also enjoy his other projects -- check them out!
lfuse:0xe1hfuse:0xddefuse:0xfe
And, to set those fuses, a command something like:
avrdude -U lfuse:w:0xe1:m -U hfuse:w:0xdd:m -U efuse:w:0xfe:m -c arduino -p attiny85 -F -P /dev/cu.usbserial-ADAPHONEX -b 19200