The SQC is a "Small Quick Change" connector. The SQC was used on the 8431 load. Bird has since standardized on the QC connector series.
The flange of the SQC connector measures 1" square whereas the standard QC flange measures 1.25" square. For this reason, the SQC and standard QC connectors are not interchangeable. A drawing of the 4100-014 is shown below.
A N-type SQC connector, part number 4100-014, is still available and can be found here: SQC 4100-014 Connector