How Do You Cut Square Holes for Balusters?

To cut a square hole for a baluster, use a hollow-chisel mortising bit, or drill a round hole and square the corners with a sharp chisel. But for 1/2″ square hollow iron balusters, you may not need a square hole at all: our T-Plug shoeless install kit screws the baluster straight down onto the tread with no hole and no shoe, for a clean look.

By Douglas Lovin, owner of Cheap Stair Parts, 20+ years in stair parts · Updated 10/21/26

Your Options at a Glance

Method	Looks	Difficulty
Round hole + base shoe	Shoe covers the hole	Easiest. What most people do
T-Plug shoeless install kit	No hole, no shoe at the tread	Easy. 1/2″ square hollow balusters only
Mortising bit (square hole)	Tight square hole, no shoe	Hardest. Needs a mortiser
Round hole + chisel the corners	Square hole, no shoe	Slow, but no special tools

Option 1: T-Plug Shoeless Install Kit

For 1/2″ square hollow iron balusters, the T-Plug shoeless install kit is the easiest way to skip shoes at the tread. A dowel screw goes into the tread and a plastic insert goes into the bottom of the baluster, then the baluster threads right down onto the screw:

1. Cut the baluster to length and file off any burrs or extra powder coat at the bottom.
2. Drill a 3/16″ hole, 1-1/2″ deep, in the tread where the center of the baluster goes.
3. Turn the dowel screw into the hole with vice grips until the tread reaches the smooth center part of the screw.
4. Push the plastic insert into the bottom of the baluster until it’s flush.
5. Thread the baluster onto the screw until all four corners sit flat on the tread and it faces the way you want.

Option 2: Mortising Bit

A hollow-chisel mortising bit has a drill bit inside a square chisel. The bit clears the wood and the chisel cuts square corners at the same time. It makes the cleanest square hole, but it needs a mortising machine or drill press, so it works best on parts you can bring to the bench, like a handrail before it’s installed. Match the chisel to your baluster size and set the depth stop before you start.

Option 3: Drill and Chisel

1. Mark the square outline of the baluster on the tread.
2. Drill a round hole inside the outline, as big as you can without crossing the lines.
3. Use a sharp chisel to cut out the corners to the lines.
4. Test fit the baluster and pare off a little more until it slides in snug.

It’s slow, but it works on treads that are already installed, with no special tools.

Or Just Use a Round Hole and a Shoe

Most installers drill a round hole and slide a base shoe over it. The hole is bigger than the bar so you can turn each baluster to line up, and the shoe hides the gap. For bit sizes, see what size hole for balusters. For the full drilling steps, see how to drill holes for iron balusters.