An engaging device in a Mass-Interconnect, which provides an apparatus and method to change test adapters for testing applications. An engaging device of a Mass-Interconnect includes an interchangeable test adapter (ITA) and a locking mechanism. The locking mechanism includes a plunger having a plunger head at a first end thereof, a leaflet insert disposed over the plunger, a sleeve disposed over the leaflet insert, an over-dead-center (ODC) link connected to the plunger at a second end thereof opposite to the first end, and a rotatable handle connected to the ODC link. The plunger, the leaflet insert, and the sleeve of the locking mechanism engage or disengage the ITA when a user rotates the rotatable handle.