Abstract: A set of interlocking wrenches wherein each wrench is configured to engage a second wrench of the set when the two wrenches are placed end to end to extend length and leverage of the first wrench. Each individual wrench has an elongated handle, a box style working head located at one end of the handle, and an open ended working head located at the other end of the handle. A recessed notch or receptacle is formed at the base of the box style working head of each wrench of the set. The notch is configured to cooperate with a jaw of the open ended working head of another wrench of the set, so that two wrenches may be placed end to end and securely engage one another. The notch has surfaces serving as stops maintaining the open ended working head in engagement with the first wrench. The second wrench employed to increase effective length of the first wrench is constrained against slipping out of engagement by the notch when the second wrench is subjected to force increasing torque applied to the first wrench.