For those of you (like me) who have trouble keeping up with all the screwy terminology out there, here is a mini-refresher course. The problem is not helped by different manufacturers/suppliers using different terms for some of the same items as well. The first pic shows a few of the different types of SS (stainless steel) hardware out there. Lowe's has the best SS assortment by far as compared with Home Depot. But if you have a West Marine or Boat U.S. store handy, they should also have an excellent assortment, although they probably will be more expensive due to the single item pricing.
1. The top row shows from left to right the following types of flat washers. A large fender washer 3/8ï¿½ x 1 _ï¿½ diameter at far left. Fender washers are extra large washers that can serve as backing plates in softer materials, or under heavy stress where a regular washer might pull out. Next to the right we have a regular 3/8 ï¿½ flat washer, then a regular 1/4ï¿½ flat washer. Then a #10 x 1 inch diameter fender washer, followed by a regular #10 flat washer. You can also use a larger diameter washer than your screw size by combining two or more washers. For example, if you needed a washer diameter the size of the 3/8 inch above with a #10 machine screw, you could use both a #10 fender washer and a 3/8' fender washer together.
2. In the second row, you see four different sizes of Nylock nuts, otherwise known as Nylon insert lock nuts. As the name indicates, these nuts have a very tight fitting Nylon insert that serves as a built-in lock washer. Thus, instead of you having to juggle three fittings (nut, lock washer, and flat washer) with your fingers in a tight spot, you only need to attach a single Nylock nut. These nuts are very resistant to coming loose, and work the same way a normal lock washer would to maintain a tight fit. From left to right, we have _-20, 10-24, 8-32, and 6-32 diameter Nylock nuts. The first number is the machine screw diameter followed by the number of threads on the screw.
3. In the third row we have several different sizes and types of machine screws (also called stove bolts) with Nylock nuts installed. At far left we have a _-20 x 3/4 inch long Phillips round head machine screw. Next right is a #10-24 x 1 inch long Phillips flat head machine screw, followed by a 8-32 x _ inch long Phillips oval head machine screw, and at far right is a 6-32 x _ inch long pan head slotted machine screw.
4. In row four we see several different types and sizes of sheet metal screws, also known as tapping screws, or self-tapping screws. At far left we see a Phillips round head _ inch diameter x 1 _ inch long screw, followed at right by a #10 x 1_ inch long flat head Phillips, then a #8 x 1 inch long flat head Phillips, and finally at far right a #6 x _ inch long pan head Phillips screw.
5. In the bottom row, we have three different types and sizes of machine screws and one bolt with conventional flat washers and lock washers attached. At far left, we have a _-20 x 2 inch long oval head Phillips machine screw, followed by a _-20 x _ inch long hex head machine bolt, then a #10-24 x one inch long Phillips oval head machine screw, and finally at far right a #8-32 x _ inch round head Phillips machine screw. As another point of terminology, when a machine screw has a hex head it is usually referred to as a ï¿½machine boltï¿½ or a ï¿½hex boltï¿½ by manufacturers and suppliers (e.g., West Marine).
The second pic below is of the very handy ï¿½Nut and Bolt Gaugeï¿½ available from a variety of sources, including Lowe's and Home Depot. It is worthwhile to note here that the length of the different head designs of screws and bolts are measured differently. For example, the length of flat head and oval head screws are measured from the top of the head to the tip. However, the length of round head, hex head, and pan head screws are measured from the underside of the head to the tip. So, if one type of screw is just a tad too short (or too long), sometimes you can find a perfect fit by shifting over to the other style.