DKS FTAB-6

A: Great question. The split tail type of mounting tab is used specifically on the type of steel door construction that features two "pans" of steel placed on top of each other that feature a return. This is referred to as "center seam" (though not all center seam doors feature the return) as seen on page 10 of the SDI Glossary (document SDI 134-2020) as seen here:

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This pan type of door might be considered an "older" type of design supplanted by center seam doors that do not have the return.

The split tail mounting tab is required to accommodate the return feature of the steel pans.

Center seam with returns is not a favorite of many hollow metal shops as this design usually complicates quick fabrication procedures.