An instrument according to the present invention comprises a casing, an exposed working head with an associated movable element, an actuating link slidably mounted relative to the casing for moving the element and an actuator mechanism with a control portion for sliding the actuating link. The actuating link is biased slidably in a first direction relative to the casing which urges the jaws, blades, etc. to a closed position. Upon radially depressing the control portion, the actuator mechanism causes the actuating link to move against the spring bias slidably in a direction opposite to the first direction. Structure is provided to selectively lock the jaws on the working head in an open position. Successive depressions of the control portion of the actuator mechanism alternatingly lock the jaws open and closed. Because the jaws are urged to a closed position, the user does not have to maintain constant closing pressure during use yet the user has the ability to easily lock the jaws in an open position.