Shafts, threads and shaft diameter
Explainer · Last reviewed 2026-08-18
The shaft is the part that actually reaches the fish, and its diameter, stiffness and tip attachment decide whether the gun's energy becomes penetration or becomes a bent piece of steel.
A shaft is a length of spring steel with a means of engaging the bands at one end and a point or a tip fitting at the other. Everything about it is a compromise between stiffness, mass and drag.
DIAMETER. A thicker shaft is stiffer and heavier. Stiffness matters because a shaft that flexes in flight loses accuracy and energy; mass matters because momentum carries penetration. But thicker also means more water drag and more energy needed to accelerate it, so a gun's bands and a shaft's diameter are matched rather than chosen independently. Common diameters run roughly from 6 to 8 mm, with heavier shafts on longer and more powerful guns.
NOTCHED OR THREADED. A notched shaft has shark-fin notches cut into it for the wishbone and a fixed point machined on the end. A threaded shaft accepts screw-in tips, which allows slip tips and replaceable points at the cost of a joint that is a potential weak point and needs checking.
MATERIAL AND HARDNESS. Spring steel that is too soft bends on rock and stays bent; too hard and it can snap. Most shafts are a compromise, and a bent shaft can often be straightened once but is never the same.
THE FAILURE MODE IS BENDING, and it usually happens on a miss into rock rather than on a fish. That is worth knowing because it means shaft damage is a function of the ground being dived rather than of the fish being shot.
Matching shaft to gun, and why it is not free choice
A shaft that is too light for the bands is over-accelerated: it flexes, it flies inaccurately, and the energy that should have become penetration becomes vibration.
A shaft that is too heavy for the bands leaves the muzzle slowly, drops over distance and reaches the fish with less energy than the gun could have delivered.
The manufacturer's specification is a genuine starting point here rather than a marketing figure, because the band configuration and the shaft mass were designed together. Divers who add bands to increase power frequently need a heavier shaft to absorb the extra energy, and this is one of the few places where a modification cascades into another one.
Inspection is simple and worth doing: sight down the shaft for straightness, check the notches for rounding, and on threaded shafts check the thread and tip for looseness. A rounded notch releases early and a loose tip is lost with the fish.
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Where it matters
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The environment that determines the failure rate.
- FAO fishing gear types and fishing technology information — Food and Agriculture Organization of the United Nations (Scientific institute)Relied on for: Spear and harpoon construction and specification.States this directlyCitation checked — the work exists and is described correctly
Related reading
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Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Spearguns and slings
The two components cannot be selected independently.
- FAO fishing gear types and fishing technology information — Food and Agriculture Organization of the United Nations (Scientific institute)Relied on for: Spear and harpoon construction and specification.States this directlyCitation checked — the work exists and is described correctly
How this compares
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Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Shafts and tips
The component record and the reasoning behind choosing between them.
- FAO fishing gear types and fishing technology information — Food and Agriculture Organization of the United Nations (Scientific institute)Relied on for: Spear and harpoon construction and specification.States this directlyCitation checked — the work exists and is described correctly
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- FAO fishing gear types and fishing technology information — Food and Agriculture Organization of the United Nations (Scientific institute)Relied on for: Spear and harpoon construction and specification.Background and mechanism onlyCitation checked — the work exists and is described correctly
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