Apparatus for fabricating a frame structure of a spacer assembly from strip stock of different metal material for use in an insulating glass unit, said apparatus including multiple work stations for treating an elongated metal strip as the metal strip moves through successive work stations along a strip path of travel, the work stations comprising: a) a corner forming station comprising: i) a punch drive for moving a die into engagement with a flat surface of the metal strip at controlled locations along a length of said metal strip to form initially notches and weakened zones of corner structures (32b-d) that facilitate bending of the metal strip into a closed multi-sided structure; ii) an adjustable stop assembly which includes a stop body and a stop body support mounted in relation to the strip path of travel and wherein the stop body defines first and second different movement limiting stop (810,812) surfaces located on different regions of the stop body for limiting movement of the die to a controlled amount that depends on a type of material of the strip stock passing through the corner forming station; and iii) a stop actuator for rotating the stop body relative to the stop body support to position a selected movement limiting stop surface in an engagement position for limiting movement of the die during a punch stroke; b) a roll forming station for bending the metal strip to form the frame structure into a channel having lateral walls (42,44) to which an adhesive is applied during fabrication of the insulated glass unit; c) a severing station for separating a lead frame structure from subsequent frame structures after the lead frame structure has moved through the corner forming and roll forming stations; and d) a control station for adjusting energy transferred during engagement between the die and the metal strip at the corner forming station based upon the material of the metal strip passing through the corner forming station by rotating the selected one of the movement limiting stop surfaces into an engagement position. a) a corner forming station comprising: i) a punch drive for moving a die into engagement with a flat surface of the metal strip at controlled locations along a length of said metal strip to form initially notches and weakened zones of corner structures (32b-d) that facilitate bending of the metal strip into a closed multi-sided structure; ii) an adjustable stop assembly which includes a stop body and a stop body support mounted in relation to the strip path of travel and wherein the stop body defines first and second different movement limiting stop (810,812) surfaces located on different regions of the stop body for limiting movement of the die to a controlled amount that depends on a type of material of the strip stock passing through the corner forming station; and iii) a stop actuator for rotating the stop body relative to the stop body support to position a selected movement limiting stop surface in an engagement position for limiting movement of the die during a punch stroke; i) a punch drive for moving a die into engagement with a flat surface of the metal strip at controlled locations along a length of said metal strip to form initially notches and weakened zones of corner structures (32b-d) that facilitate bending of the metal strip into a closed multi-sided structure; ii) an adjustable stop assembly which includes a stop body and a stop body support mounted in relation to the strip path of travel and wherein the stop body defines first and second different movement limiting stop (810,812) surfaces located on different regions of the stop body for limiting movement of the die to a controlled amount that depends on a type of material of the strip stock passing through the corner forming station; and iii) a stop actuator for rotating the stop body relative to the stop body support to position a selected movement limiting stop surface in an engagement position for limiting movement of the die during a punch stroke; b) a roll forming station for bending the metal strip to form the frame structure into a channel having lateral walls (42,44) to which an adhesive is applied during fabrication of the insulated glass unit; c) a severing station for separating a lead frame structure from subsequent frame structures after the lead frame structure has moved through the corner forming and roll forming stations; and d) a control station for adjusting energy transferred during engagement between the die and the metal strip at the corner forming station based upon the material of the metal strip passing through the corner forming station by rotating the selected one of the movement limiting stop surfaces into an engagement position.