window re & re - what screws to use? - Fiberglass RV

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Old 05-18-2009, 08:23 PM   #1
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Trailer: 1974 Trillium
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Hey everyone... Hoping for a little help here. I'm removing and resealing the windows in my newly acquired 1974 Trillium. I've got the butyl tape and 3/4 inch plywood for the wood frames. I've read the posts that recommend using SS screws but nowhere could I find reference as to the type of screws. What's on there now looks like #6, 3/4 inch drywall screws - with a counter sink head with a flat flange-type top so that they don't stick out.

Could someone our there give me a bit of direction as to what type of screws to buy? I'm not sure if these are the orginal screws or not but there doesn't seem to be a SS equivalent.



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Old 05-18-2009, 08:33 PM   #2
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Name: Rachel
Trailer: 1974 Boler 13 ft (Neonex/Winnipeg)
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If your window frames are meant to have tapered head screws (like "sheet rock" screw heads), then you might want to use them again. They would just be a "flat head wood screw."

Usually, going through thin metal on the way to wood, I would figure on using a "round head screw" which has a head with a flat bottom (where it touches the metal) and a rounded top. That's because a tapered (flat) head could wallow out the metal in its attempt to countersink itself.

Do other Trilliums have flat head screws holding the windows in? (i.e. flat top, tapered bottom to the head).


PS: Meant to add that all these types (and much, much more) are available in stainless. You can order from They have a great online catalog, or you can call them. has a good stainless fastener selection too.

Note that I'm used to ordering in the US, not Canada, so that bears checking.

Depending on where you are on the island, Sidney or Victoria might have them - check at marine stores. I haven't been there in a few years, so I don't know who is in business there now.

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Old 05-22-2009, 08:17 PM   #3
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Trailer: 1973 Compact Jr
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Umm, stainless steel screws on aluminum is a bad idea -- the galvanic action is quite high and will cause the aluminum to corrode rapidly.

Zinc-plated steel screws are much safer because the zinc will corrode but preserve the aluminum. The screws are much easier and cheaper to replace than the aluminum window.
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Old 05-22-2009, 10:10 PM   #4
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Name: Rachel
Trailer: 1974 Boler 13 ft (Neonex/Winnipeg)
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You're right in that stainless and aluminum can set up a "corrosive" reaction. Boats in salt water environments have this situation especially. We still often use stainless fasteners, but we make sure to isolate them with something like Tef-Gel, or with mechanical means (washers of plastic, etc.)

I would think that unless the trailer spends a fair bit of time in a salty environment (near the shore) it would be fine with stainless, especially if some butyl or Tef Gel isolated them from the aluminum.

Wouldn't even the zinc-plated fasteners tend to rust and leave streaks?

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Old 05-22-2009, 11:06 PM   #5
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Yes, the zinc-plated screws will rust and leave streaks once enough of the zinc has corroded away to expose the steel, but they won't cause the aluminum flange under the screw to corrode until the zinc is pretty much gone.

I live near the coast so corrosion is something I have to think about.

I hadn't seen anyone comment on using plastic washers or other ways of preventing the stainless steel screws from the aluminum flange. Remember that you would have to use shoulder washers so even the shank of the screw doesn't touch the aluminum frame.

The drawback of plastic is most such washers are not UV tolerant so they fail and fall out in a year or two. Zinc-plated screws typically last about a decade. The best solution depends on sun, water, and salt. Arizona desert -- zinc-plated screws. Arcata CA, the fog capital of the US, plastic washers (there's no UV!).
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