Felt, intake valve gallery to baffle, M14-p, 2 pieces
But why only behind the Intake valve gallery?
To block airflow so it moves to the hotter Exhaust valve gallery and passes through the gap there instead!
Holes in the sheet metal baffles behind the cylinder have a gap to avoid fretting and vibration against the cast cylinder fins.
In the area around the top of the cylinder, these felts play an active part of the cooling system.
Use ordinary rib stitch tape to re-thread in the same fashion as the torn, damaged or missing one.
Sold in a pack of two, so you'll have a spare!