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Take closer look at this photo. One side of the blast gate is threaded to fit our highly flexible hose. You can't beat this type of connection because there is no chance of a hose clamp coming loose and the hose fall off.
The other side is the standard 4" tapered male connection that fits into 4" tapered female fittings and also into 4" metal furnace duct.
Need an adapter? Try our 4” x 2-1/2”, 2-1/4” adapter #13411