Inside each damaru there’s a mantra of daka (tib.pawo) written on one side, and a mantra of dakini (tib.khandro) written on the other side.
In this video you can see how the monks of Ka-Nying Shedrub Ling monastery inscribe the mantras of daka and dakini inside the Chöd damarus:
These drums are made of high quality acacia wood selected by a senior lama of Ka-Nying Shedrub Ling monastery.
The mantras inside the drums are inscribed according to Chokling Tersar tradition by the senior monks at KNSL.
Chokyi Nyima Rinpoche personally consecrates all the damarus.