You searched for "round diffuser"
Elesa
Elesa 6531 Black Polyamide Based Technopolymer Round Knob, M6, Blind Hole
Part: BT.20 FP-M6
Black polyamide round clamping knob with M6 thread for machinery and equipment adjustment.
Elesa
Elesa 6522 Black Polyamide Based Technopolymer Round Knob, M6, Blind Hole
Part: 6522
Black plastic round knob for machinery and equipment clamping and adjustment applications.