This is what you posted:
"I wouldn't expect to purchase bolts for any critical attachment like chainplates at West Marine. McMaster Carr seems to have bolts in any category.
Why would you not purchase the West Marine bolts, but purchase McMaster Carr bolts? 316 Stainless "should" be the same no matter who you buy from. Like I posted, stainless bolts do not have a strength grade- only a material grade. Stainless is not heated treated.
Second qustion: Why do marine stores even carry 304 stainless? All nautical experts I know of recommend 316 stainless only for any boat in salt water. I am sure there are many sailors who unknowingly installed 304 on ocean going boats.
I did not say I would purchase from McMaster Carr. Only that they seem to have a good selection of bolts in many different grades. It makes sense to check with any supplier before buying.
The main reason I would not purchase bolts - or anything else - from West Marine is because I work at a much better store that is their competition.
In Victoria West Marine plays a poor second fiddle to the store I work at. We are the major suppliers to the commercial fishing fleet as well as supplying Coast Guard, Coast Pilots, Police, local ferry companies and local shipyards for both commercial and recreational boats and local municipalities with gear - and the Canadian Navy. We have an in house rigging dept staffed by a qualified rigger. We have in house splicing of any size line, some of which is up to 2" for commercial use and moorings.
To quote Steve D'Antonio in the latest issue of Professional Boatbuilder " Most stainless steel available to the marine industry and retail purchasers is 304. Stronger than 316, it is the least corrosion-resistant commonly available grade of marine approved stainless steel. While its corrosion resistance is considerably higher than that of ordinary steel, it is far from corrosion proof. The popularity of 304 in the marine trades is a function of cost and availability. It's less expensive than 316 and does a reasonably good job when not called upon to do something it was not designed for. As for availability, a 316 hex-head cap screw, say, is rarely stocked by common chandleries and must be special ordered from hardware suppliers. Most builders just go with the 304 cap screw on the shelf."
Most boats have 304 fastened hardware, 316 is rarely in production boats. For submerged fasteners bronze is a better choice. Or I suppose titanium could be used but it will be more expensive than 316.