A compound of the general formula or wherein X is O, NR4 or S and R1-R8 are as defined in the specification. A product is retained interiorly of the body, and a pump assembly fluidly communicates with the product in the body. The dry lubricant on the surface of the steel wire can be effectively cleaned by friction between the lubricant on the steel wire and the cleaning members. The throwaway insert is attached to the drill main body by insertion into the concave groove in a direction from the distal end face to the concave groove while engaging the convex portions with the guiding grooves. The pressure is estimated by generating a pump displacement control signal in a convention feedback control algorithm and using that signal together with a sensed motor speed signal and a sensed pump speed to estimate the hydraulic pressure.