When positioning the horizontal above the short vertical section, use another short vertical as a temporary spacer on the other end to guarantee the horizontal is perpendicular to the major frame. Once everything is tightened, remove the spacer.
Apply a tiny amount of silicone grease to the aluminum holes. Remove the set screw. Position the connector and use a block of wood between your hand and the connector to push the connector into the hole to avoid discomfort to your hand. Rotate the connector, if necessary, with a screwdriver or needle nose pliers as needed to make it align properly in the hole. The connector has to be below flush of the extrusion so I used a C clamp and the shaft of a 3/8" drill bit to gently squeeze the connector below flush. Gently tapping the T-nut head with the block of wood will cause it to climb the ramp built into the connector for final connector positioning. Screw in the screw just tight enough to grab the T-nut so it won't fall out. Eventual apply silicone grease to the O ring on the T-nut to allow it to smoothly enter the extrusion at final assembly.
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When positioning the horizontal above the short vertical section, use another short vertical as a temporary spacer on the other end to guarantee the horizontal is perpendicular to the major frame. Once everything is tightened, remove the spacer.
Apply a tiny amount of silicone grease to the aluminum holes. Remove the set screw. Position the connector and use a block of wood between your hand and the connector to push the connector into the hole to avoid discomfort to your hand. Rotate the connector, if necessary, with a screwdriver or needle nose pliers as needed to make it align properly in the hole. The connector has to be below flush of the extrusion so I used a C clamp and the shaft of a 3/8" drill bit to gently squeeze the connector below flush. Gently tapping the T-nut head with the block of wood will cause it to climb the ramp built into the connector for final connector positioning. Screw in the screw just tight enough to grab the T-nut so it won't fall out. Eventual apply silicone grease to the O ring on the T-nut to allow it to smoothly enter the extrusion at final assembly.