Electroimpact has retrofit two E4100 riveting gantry machines and two more are in process. These machines use the EMR riveting process for the installation of slug rivets. We have improved the skin side EMR to provide fast and reliable results. In paper 2015-01-2515 we showed the slug rivet injector using a Synchronized Parallel Gripper that provides good results over multiple rivet diameters. This injector is mounted to the skin side EMR so that the rivet injection can be done at any position of the shuttle table. The EMR is a challenging application for the fingers due to shock and vibration. In previous designs fingers would occasionally be thrown out of the slots. To provide reliable results we redesigned the fingers retainer to capture the finger in a slotted plastic block which slides along the outside diameter of the driver bearing. The various size fingers are pinned to the block in such a fashion as to allow rotation and clamping on the rivet. The clamping action is provided by opposing stacks of Belleville washers. The design of the fingers and clamping unit are shown in detail. This improvement in the injector (already reported) working with an improved finger design has provided unprecedented reliability and rivet rate.