The difference between 304 and 316 stainless steel fasteners

Stainless Steel Fasteners: The 304 Series

The 304 stainless steel fasteners series is made up of approximately 18% chromium and 8% nickel (18-8). These fasteners, which also include the 302, 302HQ, 303 and 305, are characterized by multiple variables and grades with a close chemical composition. The term “18-8” is used interchangeably and is one such characteristic used to define this series of fasteners.

There is very little overall difference in corrosion resistance among these 18-8 series types. They do, however, feature slight differences when it comes to their chemical composition, making some grades more resistant than others against particular chemicals or atmospheres. This fastener series has superior corrosion resistance and is generally non-magnetic. It is also harden-able by cold working.

The types of fasteners found in this series include:

  • Sheet metal screws: Type “A” Threads favorably used in many marine and assembly applications
  • Machine screws: flat head, oval head, pan head, truss head, flat head slotted machine screws and hex head indented machine screws
  • Bolts: hex head bolts, “Tap” head (full thread), carriage and lag bolts
  • Nuts: machine screw, finish hexagon, nylon insert lock, acorn cap, coupling, wing, “K” kep, serrated flange, tee,  thin “jam”, all metal hexagon, barrel, carriage cap and heavy nuts
  • Washers: flat, lock, fender, finish, internal / external star lock, neoprene bonding, AN flat, SAE flat and square washers
  • Socket products: These are excellent for use where corrosion resistance is required or where you have limited space. These are ideal for engines and motors. Products include socket head cap, socket set, flat socket head cap and button socket head cap screws.

Stainless Steel Fasteners: The 316 Series

The 316 stainless steel fastener series contains slightly more nickel than the 304 series, as well as 2-3% molybdenum. This gives these fasteners much better levels of resistance to corrosion than the 304 series. These fasteners are ideal of use where there is exposure to chemicals and other types of corrosive products such as chloride which tends to cause pitting.

This series offers superior performance when products are to be exposed to sea water and is resistant to corrosion in sulphuric acid compounds. These fasteners are thus best used in projects where there is likely to be exposure to direct salt spray and a variety of harsh chemicals.

The types of fasteners found in this series include:

  • Sheet metal screws: flat head, oval head and pan head screws
  • Machine screws: flat head, oval head and pan head screws. The majority of these are characterized by a “DIMPLE” or a “DOT” which assists in verifying a proper alloy.
  • Bolts: hex head, carriage and oval head strut bolts
  • Threaded rod and full thread studs: threaded rod (3 and 6 foot lengths) and full thread studs
  • Nuts: finish hexagon, nylon insert lock and acorn cap nuts. These are ideally used with Thru-Bolting applications whereby bolts, machine screws, sockets, U-bolts and threaded rods are required.
  • Washers: flat, lock and fender washers

At Marsh Fasteners, we have over 20 years’ experience as a leading source for quality stainless steel and marine grade fasteners and hardware. With our friendly and knowledgeable staff, excellent stock inventory, competitive pricing and a variety of services for all types of industries, you can rest assured that we have all of your project construction needs covered. Contact us today!

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