Set of tuning rings inserted into reed well (Bocal Well for English horn)
"Tuning Rings are important for every serious player. For a lower pitch you can pull out your staple or bocal. But this causes water and a often unstable intonation plus a lack of sound."
Oboe (5 rings) .05, 1, 2, 4, 6 mm rings (7mm diameter)
EH (3 rings) 2, 4, 6 mm rings (8mm diameter)