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Description
A pressed steel half ball, 100mm across, for domed caps on bollards and gate posts, or to weld into a full 100mm ball. This hemisphere is pressed from mild steel sheet 2 to 3mm thick, 100mm across the open rim and about 50mm high, smooth on the outside and hollow underneath. Weld it over the end of an 88.9mm tube, or onto a cap plate on a square post, for a rounded domed top. It weighs about 0.23 kg. The price shown is for one hemisphere, with a minimum order of 5.
Why choose this hemisphere
A bold domed top. On an 88.9mm bollard it overhangs a few millimetres all round for a classic mushroom-head look; on a 100mm box post it sits on a cap plate as a neat dome finial.
Seals the post. A welded dome keeps rain out of tube bollards and posts, so they do not fill with water and rust from the inside.
Light and easy to fit. At about 0.23 kg it is easy to hold in place and tack, and the 2 to 3mm wall welds without burning through.
Makes a full sphere. Weld two rims together and grind the seam for a 100mm hollow ball.
Where it is used
Street and precinct bollards, driveway gate posts, barrier and handrail posts, play equipment, garden features and sculpture, and vessel ends in fabrication work.
Specifications
| What you get | One hemisphere, minimum order 5 |
|---|---|
| Diameter | 100mm across the open rim |
| Height | About 50mm |
| Wall thickness | 2.0 to 3.0mm |
| Construction | Pressed, hollow, open underneath |
| Material | Mild steel |
| Finish | Raw, unpainted |
| Weight | About 0.23 kg |
| Fixing | Weld on |
The height is measured from the side photo and rounded, so allow a few millimetres either way.
Which post does it suit?
| Tube or post you are capping | How the 100mm dome fits |
|---|---|
| 88.9mm round tube | Overhangs about 5mm all round, a mushroom-head bollard look |
| 100mm square box | Weld a flat cap plate first, then the dome on top |
| 101.6mm round tube | Slightly smaller than the tube, weld a cap plate first |
| 76.1mm tube | Too big, choose an 80mm dome |
Is this the right hemisphere?
| You want | Choose |
|---|---|
| A 100mm hollow half ball | This hemisphere |
| A smaller hollow half ball | 80mm hollow hemisphere |
| A larger hollow half ball | 120mm hollow hemisphere |
| A ready-made 100mm hollow ball | 100mm hollow sphere |
| A heavy solid 100mm ball | 100mm solid sphere |
| Every sphere and hemisphere | All spheres and hemispheres |
Fitting and care
Clean the rim and the surface it sits on back to bright steel. Centre the dome, tack it at four points opposite each other so it does not pull to one side, then weld round in short runs, keeping the heat down on the thin wall. If the dome is sealed all round outdoors, drill a small drain or vent hole at the lowest point.
Degrease, then prime with a zinc-rich or metal primer before painting. Hot-dip galvanising after welding gives the longest life outdoors.
Frequently asked questions
Is the price for one hemisphere?
Yes, it is for one half ball, with a minimum order of 5. Use two to make a full sphere.
Is it solid?
No. It is a pressed shell 2 to 3mm thick, hollow and open underneath.
Will it fit a 100mm round tube?
Standard 101.6mm tube is slightly bigger than the dome, so weld a cap plate on first. On 88.9mm tube it overhangs a little and welds straight on.
Is it painted?
No. It is raw steel and will rust if left bare outdoors, so prime and paint it, or galvanise it, once it is welded on.
Is the rim exactly round?
Pressed parts vary slightly, so the rim may be a millimetre or two out of round. Tack at four points and ease it into place before welding round.
Ordering and delivery
Order 5 or more online, with Express UK Delivery to your site and same-day dispatch on orders before 2pm, Monday to Friday. For a larger job, call 01744 520 110 or email sales@industrialsuppliesco.co.uk and we will confirm availability and delivery before you order.
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About Us
Suppliers to Ministry of Defence, NATO, US Airforce and Most UK Councils, Schools, Universities, Hospitals & various Government departments
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Minimum order 5 pcs