Automatic (drop door bottom) seal
The Guild of Architectural Ironmongers publication 'Glossary of architectural hardware terms' defines an automatic drop (door bottom) seal as 'a seal fixed at the bottom (threshold) of the door leaf which automatically retracts from the floor as soon as the door leaf is opened by a few millimetres, and generally requires no electrical connections. These can be fully rebated, semi rebated or face fixed.'
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