Picking the Right Hardware for Your Boat
Picking the right hardware to use on your boat can be a daunting task. The biggest consideration should be what the hardware is being used for. After that you need to consider the type of material your fasteners or hardware needs to be to ensure durability. Part of this consideration is the hardness grade that the fastener is rated. The hardness grade will be related to the diameter of the bolt and the thread pitch of that particular fastener. If you are just replacing a lost or damaged piece of hardware you will want to keep in mind is the manufacturer uses SAE or Metric fasteners. If you take all of these factors into consideration you will be able to choose the right hardware to use for your project.
Hardware Application
The biggest factor in the type of hardware you need to use is going to be based on how you will be using the hardware. If this fastener is going to be used in high torque, or high force situations, you are limited to using harder and thicker fasteners to accomplish your task. If they will be exposed to harsh environments, you are limited to stainless steel to prevent rust. Manufacturers will have specification on the type of hardware they require. A great example of this is manufacturer specifications for mounting an engine to a transom. The manufacturer will have specific requirements for mounting the engine properly. Using anything other than manufacturer requirements is a bad idea, and can result in catastrophic failure.
Material Considerations
If manufacturer specifications are not available, then you may have to make some of your own decisions on types of materials to use. There are industry standards for common uses for certain applications. If your boat is used in salt water you will need to use stainless steel for almost everything. Within stainless steel there are different quality grades. These grades within stainless steel determine how corrosion resistant the steel is. For marine (saltwater) environments you should consider getting 316 Stainless Steel, or a grade with less carbon. As the amount of carbon in stainless steel reduces it becomes more and more brittle, so that also needs to be a consideration in the grade of stainless steel you decide to use. Anything less than 316 will generally rust around saltwater.
Hardness Grades
Fasteners have hardness ratings. These ratings are indicated differently based on if the fastener is metric or SAE. If the fastener is metric it has numeric indications on the head of the fastener that describe the harness rating. SAE uses lines coming from the center of the fastener to indicate the hardness rating. The number of lines are not the same as the actual harness grade. They are just an indicator for the grade. See the chart below for further clarification. The hardness grade determines the amount of force a specific fastener can handle. You will need to pick the correct hardness grade to allow for wear and tear of the fastener over time.
Fastener Diameter and Thread Pitch
The fastener diameter and thread pitch are directly related to the hardness rating. The fastener diameter is just the width of the fastener bolt including the threads. Thread pitch is the fineness or coarseness of the threads. In SAE thread pitch is measures in threads per inch. In metric thread pitch is number of millimeters per thread. The finer the thread the more surface area there is to distribute any force put on the fastener. That means for high torque or force applications you should use fine thread screws. Decorations and accessories can use coarse thread fasteners.
Metric or SAE
For general purposes, there is no significant difference between metric or SAE fasteners. If you are working on your own little project, you can more or less pick your preference. This is not the case if you are replacing a lost or damaged fastener. If you are replacing a part, you need to identify the exact item that you are replacing. That comes down to the diameter, thread pitch, length, type of fastener head. Everything about that fastener was chosen by the manufacturer for a reason and you should keep consistent if you want your engine to work how it was designed.