The four fingers of the right hand have at least one assignment each. The index finger stays over one hole, except that when E5 is played a side key at the top of the boot is used (this key also provides a C3 trill, albeit sharp on D). The middle finger remains stationary over the hole with a ring around it, and this ring and other pads are lifted when the smallest finger on the right hand pushes a lever. The ring finger typically remains stationary on the lower ring-finger key. However, the upper ring-finger key can be used, typically for B2 and B3, in place of the top thumb key on the front of the boot joint; this key comes from the oboe, and some bassoons do not have it because the thumb fingering is practically universal. The smallest finger operates three keys. The backmost one, closest to the bassoonist, is held down throughout most of the bass register. F4 may be created with this key, as well as G4, B4, B4, and C5 (the latter three employing solely it to flatten and stabilise the pitch). The lowest key for the smallest finger on the right hand is primarily used for A2 (G2) and A3 (G3) but can be used to improve D5, E5, and F5. The frontmost key is used, in addition to the thumb key, to create G2 and G3; on many bassoons this key operates a different tone hole to the thumb key and produces a slightly flatter F ("duplicated F"); some techniques use one as standard for both octaves and the other for utility, but others use the thumb key for the lower and the fourth finger for the higher.