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How to Drill Holes for Iron Balusters
To drill holes for iron balusters, mark each hole on the treads and the handrail, then drill straight up and down (plumb) with a paddle bit. Use a bit wide enough for your baluster to turn in the hole, drill 1/4″ to 1/2″ into the tread and 1″ to 1-1/2″ up into the handrail, and keep the gap between balusters under 4 inches. There’s a video at the bottom if you want to see it done.
Tools You’ll Need
- Drill
- Paddle bit (see the size chart below)
- Tape measure
- Level
- Sharpie or pencil
- Safety glasses
- Shop vac
Step 1: Mark Your Holes
Measure and mark every hole on the treads first, then on the underside of the handrail. Space them so the opening between balusters is less than 4 inches. That’s the gap, not center to center. For exact spacing and how many balusters per tread, use our baluster measuring and spacing guide.
To line up the handrail holes with the tread holes, hold a level against each tread mark and transfer it straight up to the rail. If the marks don’t line up, your balusters won’t be straight.
Step 2: Pick Your Bit Size and Depth
Your bit size depends on your baluster. For a square baluster, the hole has to be wider than the corner-to-corner width of the bar so it fits and can be turned to line up. For a round baluster, go just a little bigger than the bar. Shoes cover the extra room around the bar.
| Baluster | Paddle bit |
|---|---|
| 1/2″ square | 3/4″ |
| 1/2″ round | 5/8″ |
| 9/16″ square | 7/8″ |
| 9/16″ round | 11/16″ |
| 5/8″ square | 1″ |
| 5/8″ round | 3/4″ |
| 3/4″ square (MEGA) | 1-1/8″ |
| Where | Hole depth |
|---|---|
| Tread or floor | 1/4″ to 1/2″ |
| Handrail | 1″ to 1-1/2″ |
The handrail hole is deeper on purpose. You cut each baluster 3/4″ longer than the space between the tread and the rail, slide it up into the rail, then drop it down into the tread. The deeper rail hole is what makes room for that.
Don’t want shoes? On square balusters, you can use a mortising bit to cut a square hole instead of a round one, so there’s no gap to hide.
Step 3: Drill Your Holes
Hold the drill firmly and start slow until the bit bites, then speed up. Keep the drill plumb (straight up and down), not square to the handrail. The rail is on an angle, but the balusters stand straight, so the holes have to be straight too.
Tip: Wrap a piece of tape around the paddle bit at the depth you want. Stop when the tape hits the wood and every hole comes out the same depth.
Step 4: Clean Up
Knock off any splinters or rough edges around each hole, and vacuum out the dust. Clean holes let the balusters sit flush and help your epoxy or glue hold.
Next step: how to install iron balusters.
Watch: Drilling Holes for Iron Balusters
Drilling Holes FAQ
What size hole do I drill for a 1/2 inch iron baluster?
Use a 3/4″ paddle bit for a 1/2″ square baluster and a 5/8″ bit for a 1/2″ round baluster. A square bar needs the bigger hole because it’s wider corner to corner.
How deep do you drill holes for iron balusters?
Drill 1/4″ to 1/2″ into the tread or floor and 1″ to 1-1/2″ up into the handrail.
Should I drill the holes straight or at an angle?
Straight up and down (plumb), in both the treads and the handrail. Don’t drill square to the sloped handrail, or the balusters will lean.
How far apart should baluster holes be?
Close enough that the opening between balusters is less than 4 inches. See our baluster spacing guide for exact layouts.