A dive knife is a general tool that scuba divers occasionally use to cut
entangling fishing line or rap on theirtanks to get a buddy’s
attention. Some items that fall under this category aren’t really knives
at all, but are tools designed for specific uses underwater. Dive
knives and tools are not weapons and should never be used to harm
aquatic creatures or deface the underwater environment.
Sheath with retainer to mount it on your equipment, such as on your BCD or back of your gauge console; or on you – strapped inside your leg or on your wrist. The sheath must hold your knife securely, yet allow you to release it with one hand.
Sharp edge for cutting.
Optional and Desirable Mask Features
Titanium – very corrosion resistant and light
Metal handle butt – On larger knifes, a metal handle butt doubles as a hammer or nice solid surface for rapping on your scuba tank.
Dive knife – a stainless steel or titanium knife, usually with a sharp cutting edge and a serrated (sawing) edge. They range in size from very compact to large.
Dive tool – a dive knife with the sharp tip replaced with a prying tool.
Dive shears – scissors, good for cutting monofilament line.
Z-knives – specialized hooks with a blade for cutting fishing line or net.
With the wide variety of masks available today, it will be more difficult to decide which one you like best, rather than finding one that fits and is comfortable. Here are some tips from the Diving Locker Pro's
Start by deciding where you will wear your dive knife or tool because this may dictate what size you’re looking for. If you travel a lot, a small knife or shears are your best bet.
Once you know placement and size range, handle a variety of knives.
Evaluate the grip in your hand. If you normally wear gloves while scuba diving, test the grip with gloves on.
Release the knife from the sheath and replace it several times to get a feel for how easy it is. Do this with gloves on, if appropriate and mounted where you plan to wear it, if possible.
Choose the best knife or tool based on the features that appeal to you.
Consider getting two tools – a dive knife and shears (or a Z-knife) if you dive in areas where you may encounter abandoned fishing line.