Hex wrenches are probably the second most commonly used tool in diving. Port plugs are secured using hex wrenches and most first and second stage regulators can have their IP adjusted with hex wrenches.

Metric hex wrenches are used almost universally (with the notable exception of omniswivel). In my save-a-dive kit, I carry a small set of stainless hex wrenches, although an inexpensive set from the hardware store will do a good job too. If you can a set with chrome plating, that is nearly as good as stainless. Black oxide wrenches will work but will rust.

I use Wera 5022720001. They are stainless and come with straight and ball-end hex heads. A variation (pictured) is available with color-coded sleeves.

Ball-end hex wrenches are helpful when it’s hard to get the right angle on a hex head screw. I cut the package in two and I only carry sizes up to 6mm (1-5mm and a 6mm) in my save-a-dive kit.

Adjustable wrenches are essential for attaching and removing hoses. Cheap wrenches work great, but can jam when used around salt water over a long period of time, thanks to corrosion. Stainless wrenches are a better choice. Seadog and Heser make good stainless wrenches. Titanium wrenches are now also widely available, but excessively expensive for a save-a-dive kit (I think one is worth it for your drysuit pocket though).

I recommend carrying having two wrenches in your save-a-dive kit as you will need a pair to disassemble some pieces of gear (for example,  to remove the SPG from a HP hose).

Flush cutters are tremendously useful tools in diving, and can be used to cut zip ties, zip tie tails, bungee, cave line, and generally trim materials to your heart’s content. Good quality versions of this tool should also be able to be used like small scissors.

I use Knipex 78 03 125 flush cutters. These are made of stainless steel (which is softer than normal tool steel). Since they’re made of stainless steel, they are less likely to rust when used in wet conditions.

However, avoid using them on thick wire or metal to keep the cutting surface in good shape.

A standard BIC lighter works well to burn the ends of cave line or bungee riggings.

A windproof butane lighter is a better option if you can find a good one. Some windproof lighters need to be stored upright, and they’re a bad choice for the save-a-dive kit.

I use the TOPKAY Butane Lighters from Amazon. They’re nothing special but they work. You will need to buy Butane separately and fill them before use.

Cave line is just a diver’s term for braided nylon line. The most common use is for tying bolt snaps to hoses or gear (for example, attaching a boltsnap to the SPG hose). However, it’s the same line we use on spools or reels.

I use Powers brand #18 and #24 braided nylon line. #18 is slightly narrower and suitable for use in low-wear scenarios. Braided is preferred over twisted line for its increased abrasion resistance.

Bad cave line is substantially less durable and holds knots poorly. I can only recommend Powers brand.
Seattle Marine Supply (SeaMar) sells this line in roughly 1000ft spools, which are relatively small.

The most common use for zip ties is for attaching a low-pressure inflator to a corrugated hose and for attaching mouthpieces to regulators. Zip ties are also great for field repairs, especially if tying a cave line rigging is impractical (for example, when your gear is wet or in the water).

Get zip ties that will fit your regulator, approximately 5mm in width and approximately 20cm in length. Black zip ties are preferred, as they are UV resistant.

I usually get these by the 100 pack at a hardware store.

Philips head screws are as common in diving as they are in general use, but they are still around. That said, no toolkit of any kind would be complete without this common screwdriver.

I most frequently use a Philips head screwdriver to adjust Goodman handles.

I use a Wera 05032022001, which is a #2 stainless steel screwdriver.

Flat head screws are used occasionally in diving and this tool is also useful for light prying. It can be used to tighten hose clamps (for example, on stage bottle rigging) or to open up the Perdix battery tray, if you’re careful (although Shearwater does not recommend this).

I use a Wera 05032004001, which is a stainless 5.5mm flat head screwdriver. I would prefer a slightly wider blade, but wider blades come with a longer shaft, and they become difficult to fit into the save-a-dive kit.

Torx T10 and T20 screwdrivers are most useful for the JJ-CCR. If you’re not diving a rebreather that requires these screwdrivers, you can probably safely leave this out of the kit. 

I use the Wera 05032052001 and 05032054001, which are a stainless T10 and stainless T20 driver respectively.

You might choose to add a T30 screwdriver, but it is only used on the JJ-CCR for the screws that hold down the webbing strap on the head, so I don’t find it that useful.

Silicone lubricant is a cheap and durable lubricant suitable for dive gear that does not contact high-pressure oxygen. I use it for general purpose lubrication. It’s used for lubricating O-rings, like those on some dry glove systems.

A small set of o-ring picks is useful when replacing O-rings or for other fine poking and picking tasks.

O-ring picks should be made of brass. Brass is relatively soft, so brass o-ring picks are unlikely to scratch brass, stainless steel, or titanium.

If you need to use an O-ring pick on plastic, use a ball end pick or a spudger — brass is hard enough to scratch plastic.

A spudger is a cheap plastic pick, about the size of a small pencil. It’s used in electronics assembly to nudge things around, to poke, to prod, and to pry. They usually have a pointed end and a flat end and you can buy 30 for about $10 from Amazon.

They’re made of soft non-conductive plastic. A spudger is useful for removing O-rings from plastic or other very delicate surfaces. For example, I use a spudger to remove the O-ring in my scooter nose cone or from my camera housing.

Bungee is useful for rigging applications where stretch is desirable. The most common uses of bungee are for mounting instruments to your wrist and for the temporary stow loop on the back of your primary light.

Bungee is constructed of a braided nylon jacket over inner elastic cords, which provide the stretch.

1/8” or 3/16” (3mm and 5mm respectively) are the most common sizes in diving. A short length is probably all most people need for on-site repairs (3-5ft or 1-2m).

A black permanent marker (I use Milwaukee Inkzall) is useful for writing down the results of a gas analysis. I find these work a little bit better than the classic black Sharpie. Technically, Milwaukee calls these permanent markers “fine point.” Thinner markers wear off analysis tape easier, so they’re not my preference.

I try to have a lot of these in my save-a-dive kit since they are easily lost and they are necessary for a safe analysis.

A black magnum sharpie is useful for fixing stage and deco bottle MOD stickers that have worn off. It is wide enough to quickly replace worn markings. This is not necessary if you’re not using stage or deco bottles.

Analysis tape/analysis stickers can be simple and cheap or somewhat fancy. GUE’s tape has spaces for all the required components of a gas analysis, comes pre-perforated at appropriate points, stays on tanks when wet, and is removable without residue.

Be sure to apply analysis tape when the tank is filled, before you arrive at the dive site. Tape will not stick to a damp tank. A warm recently filled tank will take and hold tape best.

An oxygen analyzer is an essential piece of safety equipment. Buy one and carry it with you to the dive site to minimize your risk of breathing an inappropriate gas. If you have no intention of diving with helium-based gasses ever, an oxygen-only analyzer is a less expensive option. If you intend to dive gasses with helium, buy an analyzer that will analyze helium content too. 

All oxygen sensors will need to be replaced periodically, about once every year to three years, depending on your luck and how carefully your analyzer is stored. Helium sensors are quite expensive, but DiveSoft’s analyzers have a proprietary sound-based helium sensor that does not need to be replaced.

I use a DiveSoft Solo helium/oxygen analyzer.

A standard stainless weight belt buckle is useful if a dive buddy breaks theirs, but is most commonly used if you forget the buckle that retains your heater pack or corded canister battery.

It’s essential that you have a retainer here, because if you forget this buckle your battery will inevitably fall off at the end of the dive when you forget that the retainer buckle is missing.

I keep a set of 2” d-rings and thick serrated tri-glides in my save-a-dive kit so that I can fix students gear. I carry straight and bent d-rings. This is probably not necessary if you don’t work with students.

Assorted O-rings are useful in fixing leaking equipment. By far the most commonly used O-ring is for DIN regulators, as it periodically falls out. This O-ring specification is BS1806-112. Practically speaking, if you search for “replacement DIN O-rings” you’ll be able to buy a couple. Keep spares for the equipment you actually use too.

A malfunctioning low-pressure power inflator (LPI) can be dangerous, as it can auto-inflate your wing and may cause an uncontrolled ascent. If you discover a bubbling LPI before the dive, it’s best to fix the issue.

Rather than troubleshooting the problem with an old inflator (a problem that may not even be fixable at the dive site), just swap it with a brand-new inflator.

Generic inflators work on nearly all wings, and are relatively inexpensive.

At the very least, carry a few AA batteries. I recommend AA Ultimate Lithium batteries. They have a long life and can typically be used interchangeably with standard AA Lithium batteries. They are also consistently good quality.

SAFT batteries are not my favorite as they suffer from quality control issues. Counterfeit SAFE batteries occasionally will arrive when you order them online. I don’t find them as reliable as the Energizer Ultimate Lithium.

I also carry C-cells (for backup lights) and 9-volt batteries suitable for use in a JJCCR.

Bolt are useful for attaching all kind of gear that you might need to carry on a dive. They also tend to “walk away” with some frequency, or sometimes they’re lost on a dive. Fortunately, they’re relatively inexpensive. Carry one or two double enders, small boltsnaps (for backup lights or your long hose), and large boltsnaps (for your SPG).

Stainless steel snaps are preferred over brass boltsnaps, as they last longer and won’t self-sharpen. Be sure to get boltsnaps intended for marine use, as they use a stainless spring. Hardware store boltsnaps are not appropriate for diving, and will jam quickly in salt water.

Condom catheters are used by many technical divers for comfort during long dives. Although not every diver can use them, you’re guaranteed to go on a dive where someone needs one.

Carry spares if you use them yourself, and consider carrying an extra even if you don’t. If you’re not buying for your personal use (where you should buy your own size), 32mm Rochester wide-bands will fit most users.  

These are lost easily and can easily ruin a dive if they go missing. They typically come in one of two imperial sizes: 5/18-18 and 3/8-18. Metric divers are likely to use 8mm and 10mm.

Be sure to get 316 stainless, the easiest thing to do is to buy them direct from a dive shop rather than trying to source yourself.

SPGs are surprisingly easy to damage. It’s also not uncommon to notice that your SPG is reading inaccurately just before you go diving. A small stage-sized SPG will be able to fill in the role of any SPG we typically use, and therefore makes a great addition to any save-a-dive kit.

99% of SPGs are made in the same factory in Italy, so don’t worry too much about brand. Just try to get something that doesn’t have too many colors on the face, and be sure it measures pressure at least down to the 100 PSI increment.

Imperial SPGs should be used in the US, and metric elsewhere. Dual face SPGs are available and are a great option.

Book screws aka sex bolts are used to attach an inflation bottle strap to a backplate and can be lost or can break. I like to carry an extra pair since there isn’t a good alternative if you need to attach an inflation strap to a backplate.

An airspool captures the two o-rings required to seal a SPG to a HP hose. The two small O-rings are prone to leaks. The bit of the airspool between the two O-rings is typically exposed to salt water, and that salt water is trapped under normal circumstances (typically leading to corrosion). When an o-ring leaks on the SPG, I usually just replace the whole airspool and both O-rings. These are quite inexpensive and a great spare part to have in your kit.

Port plugs are easy to lose and the corresponding O-rings sometimes wear out or are damaged prior to a dive. Having at least one HP and one LP port plug available will definitely come in useful. Remember that these come in slightly different sizes: one size for LP ports to attach to LP hoses (regulators, inflators, etc) and one size for HP ports (SPG hose). They are not interchangeable, and I’d suggest carrying a couple of each.

An Overpressure Valve (OPV) is a critical component of any first stage that does not have a second stage attached to it. The two regulators typically configured in this way are the suit inflation regulator or the oxygen regulator on a rebreather. OPVs are not known for their durability and will eventually leak. It’s nice to have a spare if you’re using an inflation bottle or rebreather.

Note that a leaking OPV can be a symptom of an actual issue, and not just a leaky valve. Always check the IP when replacing a leaking OPV and never replace a leaking OPV with a port plug (this can cause catastrophic failures like burst hoses and oxygen fires).

This can be used with a valve handle screwdriver if your valve handle falls off.

Get a non-vindicator handle made of hard rubber. Black is preferred, as other colors are sometimes used for different gasses (even though this is not a recommended practice).  

A number of companies make interchangeable versions of this part.

This tool is super useful if you need to remove or replace a valve handle, or to reattach a valve handwheel that has come off. This can be done safely without emptying the tank. It’s basically a flat-head screwdriver with the center cut out.

I use the XS Scuba Valve Handwheel Tool.

An 8mm nut driver (or 5/16”, which is nearly identical) is ideal for driving hose clamps without using a flat head screwdriver. If you find yourself adjusting or removing/replacing hose clamps often, this is a great tool to add to your kit. 8mm and 5/16” are both nearly the same dimension, and will work interchangeably on most hose clamps used in diving.

I use a PB Swiss PB 8200.S 8-120, but the Klein Tools 630-5/16 is a great alternative.