Installing a half-round gutter end cap is an easy task to finish up your gutter installation. If your gutter reaches an end point where it doesn't turn a corner, you will need to install an end cap. A downspout is added to the gutters several inches interior to the end cap.
Step 1- Install the End Cap
The first step in installing a half-round end cap is to place the end cap at the end of your gutter. You can hold the end cap in place by drilling a sheet metal screw into it. Once the sheet metal screw has stabilized the end cap, use a pop rivet gun to add a pop rivet. Use your drill to add a 1/8-inch hole and then install the pop rivet inside it. Pop rivet guns can be purchased at any home improvement store and most can fit a variety of pop rivet sizes. A pop rivet is the most flush and watertight fastener that you can use for a gutter. Then you can remove the screw and following the same steps, add a pop rivet in it's place.
Step-2 Make it Watertight
Since you are adding a downspout, you don't want water to leak from your end cap. Use silicone caulk to seal the entire end cap seam and the location of the rivets as well.