підпальцева виїмка (на руків'ї ножа тощо)
fingertip formation / finger-four formation / four finger formation
finger cutout
finger grip
finger lever
finger tip control
finger-tip adjusting
have a finger on a nuclear trigger
hold a finger on a nuclear trigger
slot-type groove
spiral parallel groove
barrel groove
breechblock-stop groove
cam groove
circular groove (of ammunition)
crimping groove
dismounting groove
vertical oil groove
extraction groove
extractor groove
four-groove barrel
groove for coupling
groove