Thread: Stainless Steel Screws

Howdy,

A lot of retail chandleries do sell 304 fasteners even though they will be careful to make sure all actual fittings are 316.

I didn't know this until I worked in one for a few years.

So I found out that I had been using 304 for possibly decades without knowing it.

So it is not a really big deal I don't think. I would not hesitate to use 304 on a dayboat.

I do know that Duckflat supplies only 316.

On the other hand ... I don't know where you would use 300 screws of the same kind if you were building in the modern style using glue.

Best wishes
Michael Storer

304 is marine grade but as mentioned not best,
if harsh or constantly submerged conditions use 316

Take a small magnet with you, when shopping for stainless. Good stainless (316 or 316L) will not be attracted to the magnet, but cheaper grades like 303 and 304 will stick to it lightly (not quite as strong an attraction as mild steel). The more attraction you feel with the magnet, the lower the grade of the stainless.

The lower 300 series grades are acceptable in the marine environs, but don't like salt much and will quickly rust in brackish or sea water.

For small quantities of screws, nuts and machine screws, I use Mr.Stainless in Drummoyne. I realise that you are in SA and may not have a local branch, but small quantities are pretty cheap to post. I have seen both 304 and 316 on the shelves.
Cheers
Graeme

Howdy,

Most chandleries carry 304 for small bolts, nuts and screws. Duckflat has 316 for everything.

MIK

In general 304 is adequate in marine applications other than total submersion.
However the grade is such that you will find that they will give the tea staining trail as they deteriorate in a saltwater atmosphere.
316 is a higher grade that has better resistance to this phenomonon.
I use 316 exclusively near boats and in coastal climates generally.

Jamie

Beware of 304 in any environment close to the sea, it is a very poor choice for this application.

Worked in the metal furniture frame game for a number of years and we had to do an emergency replacement pair of sofa frames for a major manufacturer who supplied and delivered sofas to a couple in surburban Melbourne without being advised that they were for a Mornington holiday house. Inside, and 2km from the sea, the 304 mirror polished frames tea stained within weeks, and were leaving rust marks on stone floor within 6 months.

We would not do anything that would be exposed to the weather in anything but 316, because it was too hard to keep 304 clean and stain free when exposed to the elements.

As supporting evidence, when my father was fitting out a cruiser 35 years ago, he used chandler supplied "marine SS" screws, nuts and washers. Within 10 years, all the screw shanks and nuts that were covered behind engine covers, upholstery, trim etc had rusted and crumbled away, so handrails etc pulled loose without warning. All refitted with 316 items direct from the manufacturer, and 20 years on no problems at all.

Genuine 316 fasteners are about triple the price of 304 items, due to the material and machining costs, but would definitely be worth the difference over the life of a boat.

304 grade MSS is acceptable in boat building if you have a full epoxy encapulation, 316 is excellent for external use but be sure to take care to keep it dry because when moisture becomes trapped (stagnant) against the stainless steel it quickly looses its free oxygen content. The causes the passive nickel oxide surface layer on the stainless steel to dissipate and the stainless steel very quickly becomes active and begins to corrode as if it were mild steel. This is called crevice or poultice corrosion.

The best alternative is to use silicon bronze fastenings, they will not corrode and though they do not have the same strength as steel they are just as suitable once in place.