In a message dated 3/10/04 12:04:45 AM Eastern Standard Time, trawler-world-list-request@lists.samurai.com writes: > From: "Dick Schroder" <oilpans@thepoint.net> > Subject: TWL: RE: RE: Re: Twisting the heads off SS screws > > > Must be something to do with salt water. It does. Have you folks actually had this problem or just repeating what > > you've heard?? > Can't speak for others, but I have seen it many, many times over the years. Capt. Bill

"Dick Schroder" asked Have you folks actually had this problem or just repeating what you've heard?? REPLY As an installer who has twisted off a number of screw heads ( too many to count ) in both aluminum and fiberglass, I speak from personal experience. This is why I said that many SS screws simply do not have the same strength as some of the mil spec alloy screws that I have worked with on industrial and commercial jobs where we had to use certified quality components. I also know that Tefgel will make a big difference even when the hole size and crew diameter is identical. Carver sent us boats with aluminum arches and cover plates for the access holes. The fasteners were plastic. Unfortunately these often stripped the threads or sheared off the heads after three or four cycles of installation and removal. The solution was to replace them with so called marine grade SS screws. Even in fresh water the interaction of SS screws and aluminum arches is noticeable after a single year. In addition, most customers wanted any number of additional accessories mounted on the arches ranging from GPS antennas to extra alights to speakers etc. While I always used through bolts for the radars and VHF whip antenna mounts it was not always practical to cut more access holes to get at the back side of through bolts for every item. In such cases it was easier to use wood style or self tapping screws. The rule of thumb was to drill the pilot hole one size larger than you would if toy were fastening into hardwood. Same thing with fiberglass consoles and mounting everything from speakers to microphone clips or instrument bezels. If the instrument was provided with a countersunk hole for a #6 screw it was not always possible to upsize to a #8 or #10. Quite often the #6 screw would twist off unless you drilled out the pilot hole oversize. In addition you had to countersink the edge of the pilot hole or the gel coat would chip. Electrolysis and galvanic action does not figure when placing a SS screw into fiberglass but an effect similar to galling does. Galling can be reduced with use of lubricants. Even dry gels or soap will ease the friction while facilitating the thread cutting action of a self tapping screw being run into the 'glass composite. Regards Arild --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.588 / Virus Database: 372 - Release Date: 2/13/2004