An arrowhead is a four-sided pyramid welded or screwed to the top of a palisade spear shaft. Cast iron versions are the original heritage detail, still made by foundries in Victoria and NSW. Pressed-steel versions are the modern equivalent, cheaper and lighter but visually identical from any distance over 2 m. Either way, the arrowhead carries the decorative weight of the whole fence: the spear shafts are functional, the tips are the styling.
Standard dimensions for residential heritage work: 40 mm square base, 120 mm tall, with a decorative collar 15 mm tall projecting 3 mm beyond the pyramid base on each side. The collar reads as a small step where the pyramid meets the shaft and softens the visual transition. For larger commercial palisade, base widths step up to 50 mm or 60 mm with proportionally taller pyramids; the base width rule of thumb is roughly 1.6x the shaft width (40 mm base for a 25 mm shaft).
Finishing matters. Cast arrowheads come raw and need hot-dip galvanising with the rest of the panel, then powder-coat. Cheap aftermarket arrowheads sometimes ship pre-zinc-plated and powder-coated; these fail in 5 to 8 years on coastal sites because the zinc plating is too thin for C4 to C5 exposure. CAD60's spear-top models let you toggle between crimped tip, cast arrowhead, or no tip per drawing, and the dimension lines pick up the chosen tip's height automatically.