Timber stair spindles: types, how many, and how they fix
Parts Glossary & Jargon Buster
Written by Scott Jones, The Stair Guys, independent staircase measuring and sourcing specialists·Last updated
Spindles, or balusters, are the uprights that fill the gap between the handrail and the stair, and they do two jobs at once: they are the guarding that stops anyone falling through, and they are a big part of how the staircase looks. There is more choice here than people expect, and a bit of logic to how many you need and how they go in.
The styles
The plainest is a square-section spindle, clean and modern. From there they get more detailed: stop-chamfered (the corners taken off along the middle, left square at the ends), chamfered and fluted (with grooves run down the faces), and the various turned patterns shaped on a lathe, from restrained Georgian and colonial profiles to the spiralling barley twist. The style sets the character of the whole balustrade, and mixing in the odd square newel or a turned feature spindle is common.
How many
The usual arrangement is two spindles to each tread, with a single spindle on the tread that carries the newel. That two-per-tread spacing is not arbitrary: it comes out close enough to keep the gaps within the guarding rule, which is the next point.
How they fix, and the spacing rule
A spindle is held top and bottom. At the top it sits in a groove run along the underside of the handrail; at the bottom it sits either in a matching groove in a baserail (on a closed-string stair) or directly onto the treads or a capping on the string (on a cut-string stair, see cut string vs closed string). Between each spindle, short lengths of infill called fillets fill the rest of the groove, and it is the fillets that set and hold the spacing.
That spacing is governed by the guarding rule: the gaps must be small enough that a 100mm sphere cannot pass through, so a small child cannot slip between the spindles. Two spindles per tread normally achieves it, but on wider treads or unusual layouts it has to be checked, which is covered on the guarding page. For metal instead of timber, see metal spindles.
Frequently asked
How many spindles do you need per stair tread?+
Usually two spindles per tread, with a single spindle on the tread that carries the newel post. That two-per-tread spacing normally keeps the gaps within the guarding rule, but on wider treads it should be checked, because the gaps must be small enough that a 100mm sphere cannot pass through.
What are the different types of stair spindle?+
They range from plain square spindles, through stop-chamfered (corners taken off the middle), chamfered and fluted (with grooves down the faces), to turned patterns shaped on a lathe such as Georgian, colonial and barley twist. The style sets the look of the whole balustrade, and spindles come in timber, metal or glass.
How far apart should stair spindles be?+
Close enough that a 100mm sphere cannot pass between them, which is the guarding requirement designed to stop a small child slipping through. In practice two spindles per tread, with fillet strips setting the spacing, usually achieves it, but it should be checked on wider treads or unusual layouts.
Related guides
- Staircase parts glossary and jargon busterPlain-English definitions of every staircase part and the trade jargon you meet when buying one: treads, risers, strings, newels, spindles, nosings, winders, tenons, and the difference between bespoke and made-to-order.
- Is a newel post structural? Yes, usually, and here is whyA newel post is typically structural, not just decorative. The strings frame into it and it is notched over the trimmer at the floor opening, so it helps hold the staircase together and ties it into the structure. That is why you cannot simply remove or move one.
- How a wooden staircase is put together, and why stairs creakA traditional timber staircase is a joinery assembly, not a nailed one: treads and risers are housed into grooves in the strings and locked with glued wedges and glue blocks. Most creaks come from one of those working loose.
- Feature bottom steps: bullnose, curtail and D-endThe bottom step is often shaped as a feature. A bullnose has a rounded end that returns to the front, a curtail wraps around the newel in a scroll, and a D-end curves at both sides. The shape sets the tone at the foot of the stair and where the bottom newel sits.
- Timber handrail profiles: mopstick, pigs ear, and wall vs balustrade railsHandrail profiles are the shapes a handrail is milled to. A mopstick is round and easy to grip, a pigs ear (lambs tongue) is a slim rail fixed straight to the wall, and a grooved profile carries the spindles on a balustrade. A wall-mounted rail and a balustrade rail are different jobs.
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