Modular medical instruments and kits are provided, having, a tool body portion with a first mating element at one end. A removable and replaceable modular end effector having a second mating element is matable with the first mating element. The instrument further includes a selectively engageable locking mechanism having a lever arm with a first portion associated with the body portion and a claw portion matingly engageable with a portion of the second mating element of the end effector, the locking mechanism being effective to secure the end effector to the body portion of the modular medical instrument. The invention can be particularly useful for providing a secure connection between the modular end effector and the body portion, yet provide ease of interchangeability between modular end effectors.