How to Attach Round Posts to Stair Treads

Measure the depth of the stair treads and mark the centers at the edge of the step, beginning on the stair tread above the bottom newel post and ending at the tread before the top newel post.

Measure from the riser to the center marking on the tread and mark the halfway point with a pencil. Measure from the edge of the step to the center marking and mark the halfway point with a pencil. These marks designate the point at which the balusters set into the tread.

Place a 4-foot level on the baluster mark, standing straight up to the handrail. Mark the underside of the handrail with a pencil when the bubble centers in the level.

Equip a power drill with a spade bit that matches the size of the peg at the bottom and top of the stair post. Drill a hole 3/4 inch deep into the stair tread and 1 inch deep into the underside of the handrail.

Clean the wood debris out of the holes with a shop vacuum.

Loosen the bolt that holds the handrail to the newel post with a wrench. Place the stair post into the hole in the tread and the corresponding hole in the handrail, while a helper lifts the stair rail, to test-fit the stair posts. If the post fits too tightly into the hole, sand the hole with 80-grit sandpaper to widen it. If the stair post is too loose, insert a wood shim to fill the excess space.

Coat the peg ends and insides of the holes generously with epoxy adhesive, working on one tread at a time, which requires two stair posts. Insert the adhesive-coated ends of the stair post into the tread hole and underside of the handrail while a helper lifts the rail. Repeat for each stair post.

Place a cloth-wrapped piece of wood on top of the handrail after every two steps have stair posts installed, and tap the wood with a rubber mallet to force the posts into the holes.