* * *
OffCenterHarbor.com is a membership website with over 1,000 videos and articles on boat handling, repairs, maintenance, boat building, dream boats and more.
Sign up above to learn more, and get 10 of our best videos.
* * *
Email This Page to a FriendPreview: Fasteners & Fastening, Part 1 – Naming of the Screw
March 3, 2016
Get up to date on today's fasteners and their specific uses.
– Fasteners in the boat shop are a real trick. What kind of metal might you be wanting to use? What kind of tip actually drives those fasteners properly? What kind of head style are you looking for? What’s with all these different size fasteners and machine screws, self-tapping screws, and wood screws. We’re going to take a minute and just talk about all these things and see if we can’t demystify some of the fastener questions you guys may have. So the first question is, what type of metal am I after with a fastener? And you know there’s lots of different options out there. Typically, any box that you grab is going to have the type of metal right in the upper left hand corner here. Silicon bronze, we’re looking at a silicon bronze slotted round head machine screw, size and length. Okay, very typical in the boat shop. A lot of boats were fastened in completely silicon bronze through and through, traditional boats, whether they were bronze through bolts, bronze keel bolts, its a very highly, anti-corrosive metal. The price of silicon bronze has gone through the roof, over the last 10 years and it’s a very expensive metal to buy, but there again, kind of top quality stuff. Another just very common metal fastener is stainless steel. There are different grades of stainless steel, and that’s important. 18-8 is the type of stainless steel here, which is just your kind of generic. Used for any number of things. Not a very highly anti-corrosive stainless. Or we would move into more of a 316 stainless steel. Just a very different type of grade, much better for exterior use, on polished hardware. You can’t tell the difference visually between the 18-8 and 316 stainless steel. You really need to keep track of what you’re look at on the box, 18-8 stainless steel in an exterior application will slowly and eventually bleed rust. Even if it’s highly polished when it’s put on to the deck of a boat in an exterior application it will eventually start to bleed rust, and then it has some iron in it. You actually take a magnet and you can magnetically tell the different between 8-18 and 316 stainless steel, and the 316 stainless will not adhere to a magnet in any way, and the 18-8 is actually quite a magnetic draw, which tells you there’s a level of iron in there, but again in an exterior application, isn’t wonderful. 316 is sold as a very highly anti-corrosive metal. One thing that stainless has a problem with is what’s called crevice corrosion. Any kind of stainless, when it is buried and completly isolated from any kind of oxygen, will get what’s called crevice corrosion and it’s little pits that develop over a number of years, and eventually the fastener has the potential to fail. Around the shop here, very typical fastener used to be just steel, sheet rock screws. We are slowing moving away from these in kind of general purpose construction. You can see anywhere around the boat yard there are work benches screwed together, handrails, a lot of things that are meant to go together and come apart based on the reconfiguration of the shop or setting up and breaking down a mold. We’ve moved away from sheet rock screws and more to these for general constructions purposes, these grk star-drive screws. Wonderful for scaffolding. These kind of washer-headed screws are great for drawing two pieces of wood together and not sucking the head in so deep that you can never find the fastener again or even know that it’s there. So again, metal types: sheet-rock screw, steel sheet-rock screw. I would never leave something like that in a boat; in an interior or exterior application. Grk screws. They are coated, but you can see there that as those screws get driven in and out that does get compromised and you can see that there isn’t a gold color where the drive is. That will eventually start to rust and rust will bleed through paint, it’ll blow off fiberglass. Metal in a boat is not a great thing. We certainly do use these screws when we’re actually drawing some pieces of wood together that are being glued in a corner post or something. Especially in a wood composite type construction where the screws will be removed and not in the structure at all, but you basically would use them in a pattern where they can be plugged and removed. Plugs put in their place and it would give you a traditional look as if that corner post were fastened with fasteners, but there is no metal there. They do make these grk screws in stainless steel and again, I would look for a 316-grade stainless steel if you’re gonna leave it in a boat in any kind of application. Basically, you don’t want to mix and match your fasteners with the type of piece of hardware that you’re actually securing it to. If you have a bronze cleat, you want to be looking at a bronze fastener. If you’ve got a stainless cleat, likewise. Mixing metals often times leads to trouble with corrosion, electrolytic action, where electricity flowing through salt water reacts in way where less noble metals tend to start to disappear. That’s why you see zincs and sacrificial metals on types of boats. The key to starting with anything on a boat is to make sure that you’re using like metals with like pieces of hardware. It’s very easy to create a battery by using very dissimilar metals, especially when you introduce salt water in a salt water environment and it induced corrosion in any type of metal a lot more quickly than it otherwise would be. Other metals that you may find that are very anti-corrosive yet very expensive are manill And titanium. Both of them very anti-corrosive and made, but very hard to get your hands on in any kind of quantity without spending a fortune for them. So again, the 316 stainless, great for exterior use. The 18-8 stainless steel, something that I would certainly use on the interior of a boat where it’s dry, more climate controlled, but in any kind of a damp environment, I wouldn’t touch it. Silicone bronze can be used anywhere and anyhow. It’s a very strong metal. It’s a very anti-corrosive metal and just kind of a standard in the marine industry. The next thing with any kind of fastener, is what kind of driver tip is used. Traditional slotted drive, star drive’s in the middle here, and then a conventional Phillips head. So slot is definitely a more traditional look. Nice thing about a slot head, especially a flat slot head, something that may be used in planking or more of a structural fastener, is that anything that’s been plugged, typically, whatever the plug goes in with, whether it’s varnish, shlack, polyearthing, glue and hypoxy, fills that slot with mong and a slot, unlike any other fastener, is easy to remove that with an ice-pick or a smaller slot head screw driver to get that head cleaned out so you can back it out years down the road. Not something that’s as easy to do with a star-drive or a Phillips head driver tip. Whatever head driver type, it is very critical that the bit that you drive them with, is sized for that fastener. In star drives, you wouldn’t think that there would be a whole lot of difference between these two tips. While this tip may fit into a fastener and turn it, it doesn’t need to be much too small to immediately strip that. That is the right size tip for that head and this is the right size tip for this head. It wants to seat nice and snug and whatever driver tip that you’re using, you know, bits that go into a drill or whether you’re using screw drivers, screw drivers are very specific tip size and on this set, the number of the tip is right on the end of the screwdriver. And that goes for Phillips screwdrivers as well as these slot head screwdrivers. You see a 3/16, 1/4, and 5/16 slot and not only are they wider, but the tip is also thicker. So the bigger the screw, the bigger the screwdriver you wanna use to drive it. You want that nice and snug and seeded into the head of the fastener as best you can. These are torques drivers, it’s just the style of the driver tip and they are numbered. Torques T-15. This is a T-20. That’s a T-25, pardon, and a T-30, Phillips tips. Again, you wouldn’t think that there would be a whole lot of difference between these two. This is a PH1 and a PH2 and you really wanna take your fastener and check what bit seeds most properly into it. The surest way to strip a fastener is to be using and improper driver tip. Now while both these fit in, you can see that the P2 is the bigger of the two and fills that more completely and gives you more surface area on that Phillips head. That’s the one that you would wanna use. So let’s talk about screw gauge. There’s a lot of information on these boxes. The metal type in this case is 18-8 stainless steel. In the upper right hand corner, it tells you how many are in this box. There’s 100 in this box. The next is slotted. That is the driver head style. Slotted. This denotes the gauge, it’s a number 4 gauge. A number 4, they start small, small number, small size. Big number, big size. This is a number 4, one inch long, flat head tapping. Okay, so let’s talk about that. There’s 100 of these in the box. The driver head type is a slot. It’s a number 4 gauge, which is pretty small. It is one inch in length. The head style is flat which means that it has a little bit of a countersink but a flat head and the thread is tapping which means that there are threads the entire length of it. Going down the line here what are we looking at? Number 8, 18-8 stainless. There’s 100 of them in here. It’s a number 8, you can see it compared to a number 4. And we’re getting bigger. It’s a flat head tapping, it’s an inch and a half long. So 8, here’s a number 10, here’s a number 12, here’s a number 14, and here’s a number 20. Here what I want to emphasize is more screw gauge, from small to big. The number 8, 10, 12, 14, and a number 20, the gauge size, not the length. This is a 20×3 inch long, this is a 14×1 inch long, this a number 10 by inch and a half. As the number goes up, the diameter of the fastener goes up. So last thing I want to talk about is head type or head style. Now forget about the driver mechanism but the shape of head. This is your most common, it’s a flat head and the top of the fastener is completely flat and it’s got a countersink. This would be used to drive two things together, possibly be bunged and concealed and buried. Okay, the next style which is close to that, but not quite, is what’s called an oval head and it’s just a very very slight camber, still with a countersink, something that you would use to draw two pieces of wood if you wanted a very shallow head exposed, very low profile. Next is a round head and that is a very, almost semicircular head shape. That would be used where you’re full on leaving the head of that exposed and very similar to the round head but a little bit different is a pan head. A pan head is again, a shallower dome, but it has this kind of shoulder. And you can see the difference between a round head and a pan head is very, they’re very close, but again, different head type and something you would commonly find at a hardware store. Lastly, is a hex cap and that would be something you could get a socket or a wrench on. There are more head types than this out there, but these are the most common and while here I have a machine screw and a tapping screw and a wood screw, all of the different thread types whether it’s a wood screw, a tapping screw, or a machine screw are available in all of these head types. Lots of information, lots of different things going on in the fastener world, whether it’s driver tips, head styles, gauge of screw, what you might use to drill and countersink for them. I hope this little chat kind of demystified some of that and help make sense of different metals and different fasteners that are available.