Things You'll Need
If you look at rectangular sheet metal duct work, you will notice each joint's connection looks as if it has a band of metal cinching the two joints together. This connection is actually made up of a few different components -- S-slips and drive cleats. S-slips look like the letter "S" -- they create two pockets that allow the ducts to slip together. Drive cleats hold the ducts together to prevent each from coming out of the S-slip.
Examine your sheet metal duct work. On each end, two opposite sides will have raw edges and the other two opposite sides will have a hemmed edge. The raw edge is what the S-slip slides on, and the hemmed edge is where the drive cleat will slide on once it meets up with the hemmed edge on the successive piece of duct.
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Measure the length of the raw edge. Subtract 1/2-inch and cut two S-slips at this measurement. Tap them onto each of the raw edges on one end of the piece of duct work. Notice you now have a pocket for the raw edge of the piece of duct you are connecting to slide into.
Slide both raw edges of the piece of duct work you are connecting into the pockets of the S-slip on the first piece of duct work. The hemmed edges of both pieces of duct work will butt up tight together.
Measure the length of the hemmed edges, add two inches to this measurement and cut two drive cleats at that length.
Slide one drive cleat onto where the hemmed edges meet. Tap it up with your hammer until 1 inch sticks up above and below the duct work. Tap these ends until they lay over the top of the S-slips. Repeat this process for the other drive cleat on the other side of the duct work. Notice that the two joints of duct work can no longer pull apart because they are locked into place by the drive cleats.
You may wish to caulk the seams where the S-slips and drive cleats meet the duct work. Air leakage can occur here in small amounts, and sealing these seams with caulk will reduce that leakage.
Wear gloves when handling duct work and other sheet metal components. The duct work is extremely sharp and may cause serious cuts or other injuries.