Short answer: for most Australian reef diving a 16 mm band on a 7.5 mm shaft is the do-everything setup. Drop to 14 mm & 7.0mm shaft for small guns and small fish or an easier load, and double bands for bigger fish and Bluewater. Band diameter, the number of bands and your shaft size all work together, so match them as a package rather than chasing one big number. The chart below gives you the pairings at a glance, and the notes explain how to fine-tune from there.
What band size actually means
Speargun rubbers are latex tubing, and the size on the label is the outer diameter of that tubing. A thicker band stores more energy, so it drives the shaft faster and hits harder. It also takes more effort to stretch, which means a harder, slower load-up and more strain on you between shots. The art is picking the smallest band that gives you the power you need for your target, because a gun you can load cleanly and comfortably is a gun you shoot accurately.
Wall thickness matters too. Two bands both marked 16 mm can pull differently if one has a thicker wall, so stick to a known brand and a consistent spec once you find a load you like.
The chart
Gun length
Typical target
Band diameter
Bands
Shaft
60–80 cm
Small reef, estuary, dirty water
14 mm
Single
7.0 mm
90–100 cm
Reef all-rounder
14-16 mm
Single or double
7.0- 7.5 mm
100–110 cm
Reef and light Bluewater
14-16 mm
Double
7.0- 7.5 mm
110–120 cm
Bluewater pelagic
16 mm
Double
7.5 mm
120 cm+
Heavy Bluewater, big fish
16 mm
Double or triple
7.5–8.5 mm
Use these as a starting point and adjust for your loading strength and how far you actually shoot. When in doubt, go one size lighter and shoot more accurately.
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Band diameter, size by size
14 mm. The easy-load option. It suits short guns, small reef and estuary fish, younger or newer divers, and anyone who wants a comfortable load for a long session. Less power, but plenty for the fish it is meant for. Less recoil and laser accuracy
16 mm. The all-rounder and the most common band on Australian reef guns. It pairs with 90 to 110 cm barrels for a load that most divers can manage while still driving a mid-weight shaft with authority.
18 mm. More power for bigger reef fish and light Bluewater but rarely used these days as most divers use small bore 16mm instead. Expect an increase in recoil usually and harder load-up, so build the technique before you commit to it.
20 mm. Almost non existent these days due to the difficulty in loading and intense recoil. The heavy hitter for Bluewater and big fish, on thick shafts and long barrels. Strong loaders only, and often paired with a loading assist. Overkill on a reef gun.
[tip]Two 16 mm bands almost always beat one 20 mm band for the same total power. Doubles share the load across the shaft more evenly, load more smoothly and are easier to tune than a single very thick rubber.[/tip]
Single bands or doubles?
Once you are past a 90 cm gun, you can get the same power from one thicker band or two thinner ones, and doubles are usually the better answer. Two 16 mm bands load more smoothly than a single 20 mm because you draw each one separately, they spread their pull across the shaft for a straighter launch, and you can even load just one band on an easy inshore day to soften the gun. A single band is simpler and lighter at the muzzle, which some divers prefer on short reef guns where quick handling beats outright power. As a rule, stay single up to about 100 cm and general reef work, and step to doubles when you want more punch or you are moving up to bigger fish.
Roller guns are different
Roller rubbers usually run thinner than the equivalent railgun band because they work over a much longer stroke, so they keep pulling further through the shot. A 105 cm roller might use a band that looks light next to a railgun of the same length yet still hits harder at range. Follow the diameter your specific roller is designed for rather than copying a railgun spec across, and see our roller speargun guide for how the mechanics change the numbers.
Match the shaft to the band
Power without a matching shaft is wasted. A thin shaft driven by heavy bands can flex or whip and lose accuracy, while a thick shaft on light bands is slow and drops off at range. Keep the pairing sensible: 7mm shafts with 14 mm bands, 7.5/8.0/8.5 mm shafts with 16 mm doubles. If you are choosing a whole new setup, our speargun size guide ties gun length, shaft and bands together.
When to replace your rubbers
Latex does not last forever, and a tired band quietly robs you of power long before it fails outright. Replace your rubbers when they lose their snap, when the surface goes dull, chalky or cracked, or when you spot any nick or thinning near the wishbone, which is exactly where bands let go under load. Sun, heat and ozone are what kill them, so store your gun and spare bands out of direct light and away from petrol and oil. As a rough guide a hard-used band has months rather than years of peak life in it, so treat rubbers as a consumable and keep a spare set in your kit.
Getting the length right
Diameter sets the power, but the cut length sets how much of that power you actually get, and how hard the gun is to load. Too long and the band is slack and weak. Too short and you will fight to load it and wear it out fast. Once you have picked your diameter from the chart above, work out the exact cut length with our speargun rubber length calculator, then check your loading technique in the safe loading guide.
Need a hand pairing bands, shaft and gun? Our team dive these waters themselves and are happy to sort you out.
