This is the disc that sits above the flame and spreads it out. It is held in place by leg-like clips.
There are three types available:
Omni 2: This has a spring attached. It fits Omnifuel stoves made after around 2016. It also fits the Primus Multifuel 3.
Omni: This fits Omni and Multifuel stoves made before around 2016) and has a sort of keyring attached (or on older stoves, nothing at all).
Vari: This is a completely different shape to the others and fits Varifuel, Easyfuel, and Multifuel (Himalayan).