No matter how well you build a wooden fence gate, they all share a common problem over time — the tendency to sag over time.
A sagging gate doesn’t just make your fence look old and unattractive — it’s also a hazard for children and pets.
Wide gates are no exception, and possibly are more susceptible to sagging. For example, this fence gate is five and a half feet wide, and I’ve tried everything over the years. I replaced the hinges with larger hinges. I installed the steel braces in each corner. Still, it didn’t work.
Instead of fighting gravity, prop the sagging gate up when it’s closed or open with a caster.
The caster is made from a simple two-by-four pressure-treated block. Here’s how to build it:

Cut a notch in the back of the two-by-four pressure-treated board to create a shoulder so it rests under the horizontal rail of the gate.

Then, cut another notch in the bottom to hold the caster. Drill a hole through the notch for a coverage bolt to go through to secure the caster to the block.

Finally, secure the caster block to the horizontal support board with four two-inch long galvanized screws.
Now when the gate is open or closed, the caster, not the hinges, completely supports it.
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