Yep, I've been through the problem of "matching" brass and bronze. First of all, I feel that you should avoid yellow brass fasteners at all costs. Lacqured or not, you just cannot see where under the head that the lacquer has been removed. Once sea water gets into yellow brass the fastener can rapidly erode away. Yellow brass screws only belong in non-sea water environments. I'm guessing that your brass frames are not yellow brass but naval brass (still not a great resistant metal to marine corrosion
but better than yellow brass).
Here is how I "match" different alloys which are allowed to come in contact with each other in the presence of sea water. Dip up a cupful of clean seawater and partially immerse your test metals (fasteners, or whatever). Use your DVM to measure the relative potential between any two metals. I feel that if you obtain readings around 60mV or less then you will not experience rapid degreadation between the two. Of course if you are in the Carribean then you have saltier sea water than we do on the Pacific and you would want to strive for a smaller milli-Volt reading.
Like me you will probably be surprised at the variation that you will observe (as well as the lack thereof with a good "match") I've been able to match some bronze alloys with 304 or 316 S/S with less than 30mV difference, for example.
You can buy a pound of coated deck screws for six bucks. You can pay more by buying coated S/S deck screws buy why? In that particular case I think that the buyer thinks that he is getting a more robust fastener yet, if you think about it, either the coating is not necessary or it is. If the coating is necessary then why use S/S when stronger steels are available which are vastly cheaper to manufacture? As long as the barrier coating does not fail you get a better alloy for a fastener than S/S. Remember that S/S is not particular strong or hard or forgiving in the stress/strain failure curve as compared even with mild steel
. Most people confuse the toughness (truly a metallurgical term) with hardness. You would never, for example, want to fabricate a motor
mount from S/S you would use mild steel which is very tolerant of vibration without stress fracturing as is S/S.
I am using Phillips 11 KwickTap 3/16" X 3" flathead fasteners (normally used for concrete/masonry fastening) to attach teak
handrails because the heads just fit inside a 3/8" counterbore (for the plugs) yet they are rated at 90lb load each with a 4:1 safety
factor. To get that rating with S/S I would have to use larger plugs and fasteners (#14). I don't know what is the coating on these babys yet so far I have not scraped or dinged the coating off of them. I've used them on metal and treated wood exposed outside near the seawater with good results so far. THESE screws are NOT cheap
...they are 9 to 10 bucks for 25 of them. The threads look good for both wood and fiberglass
and, yes, I do still drill pilot holes even for those screws claiming not to need them. Why unnecessarily stress hardwood?
What do you think?