You walk into a dive shop and quickly find that not all dive knives are the same. The steel grade alone can mean the difference between a blade that lasts a season and one that lasts a decade.
The two grades you'll see most often are 304 and 420 stainless steel. Both are marketed as corrosion-resistant, both look similar in the display case, and both will cut through fishing line in an emergency. Understanding what sets them apart is the fastest way to buy the right dive knife the first time, and avoid an expensive mistake.
1. What Is 420 Stainless Steel?
420 stainless steel is the most common grade in entry-level dive knives. It contains a higher carbon content than 304, which makes it easier to sharpen to a very fine edge. A 420 blade can get genuinely razor-sharp with minimal effort, which is why it's popular with divers who want a tool they can maintain at home with a basic sharpening stone.
The trade-off is corrosion resistance. 420 steel holds up well in freshwater and light saltwater use, but with repeated saltwater exposure and inadequate rinsing, it can develop surface rust over time. For recreational divers who dive occasionally and rinse their gear thoroughly after every dive, 420 is a practical choice.
Recommendation: Saekodive Edge 420 S.S. Dive Knife - Regular price $51.95 USD
2. What Is 304 Stainless Steel?
304 stainless steel is one of the most widely used grades in marine applications, and for good reason. It contains a higher chromium and nickel content than 420, which gives it superior resistance to saltwater corrosion. A 304 blade handles repeated ocean exposure far better, resisting the surface rust that can quietly degrade a 420 knife over time.
The trade-off is sharpness. 304 is softer than 420, which means it won't reach the same razor edge and will need more regular sharpening to stay effective. For frequent saltwater divers, technical divers, or anyone who wants a blade that stays rust-free with minimal fuss, 304 is the smarter long-term choice.
Recommendation: Saekodive Ares 304 S.S. Dive Knife - Regular price $51.95 USD
3. Which One Should You Choose?
The honest answer depends on how and where you dive.
If you dive in freshwater or are an occasional ocean diver who rinses and dries gear thoroughly after every dive, a 420 blade gives you a sharp, easy-to-maintain tool at a lower price point. If you're a regular saltwater diver, dive in warm-water environments where corrosion accelerates, or want a knife that holds up with less maintenance, 304 is the better investment.
Both grades have a place in the water. Take the time to choose the right steel for your diving, and your knife will be ready every time you are. Happy diving!